stream: keep webstream stream states in fast-mode objects

[mcollina]

While profiling short-lived streams (the per-request create → few chunks → close pattern), createReadableStreamState showed up at 20% self time. The cause: the per-stream state records are object literals with __proto__: null, which V8 creates as dictionary-mode objects — roughly 50x slower to allocate (~500-1500ns vs ~30ns), and every subsequent property load on them is a dictionary lookup. These records back every hot path, so both construction and per-chunk [kState] accesses have been paying for it.

The first commit replaces the four per-stream state literals (and their nested transfer records) with classes whose prototype has a null prototype: instances stay in fast mode, while Object.prototype remains excluded from the lookup chain, preserving the pollution protection the literals were there for. Every field ever assigned is declared up front so the shape never transitions. (The controller and reader states were already plain literals and unaffected.) It also adds benchmark/webstreams/lifecycle.js covering the short-lived stream pattern that exposed this.

The second commit removes the per-chunk PromiseWithResolvers for transform sink writes parked on backpressure: the writable controller's write reactions exist before the write algorithm runs, so the parked-write continuation can wire the perform-transform promise directly to them via the parked-result sentinel introduced in #65143, dropping the promise record and the thenable adoption hop.

Results (30 runs, all 36 rows significant at ***, no regressions — full table below):

                                                                       confidence improvement accuracy (*)    (**)   (***)
webstreams/creation.js kind='ReadableStream.tee' n=50000                      ***     71.39 %      ±11.02% ±14.79% ±19.52%
webstreams/creation.js kind='ReadableStream' n=50000                          ***    138.13 %      ±14.29% ±19.14% ±25.17%
webstreams/creation.js kind='ReadableStreamBYOBReader' n=50000                ***     74.72 %       ±9.66% ±12.97% ±17.11%
webstreams/creation.js kind='ReadableStreamDefaultReader' n=50000             ***     75.04 %      ±11.10% ±14.87% ±19.58%
webstreams/creation.js kind='TransformStream' n=50000                         ***    133.64 %       ±8.61% ±11.46% ±14.94%
webstreams/creation.js kind='WritableStream' n=50000                          ***    204.00 %       ±7.70% ±10.26% ±13.37%
webstreams/encoding-streams.js len=1024 kind='decode' n=100000                ***     57.21 %       ±3.11%  ±4.15%  ±5.42%
webstreams/encoding-streams.js len=1024 kind='encode' n=100000                ***     31.57 %       ±1.86%  ±2.48%  ±3.24%
webstreams/encoding-streams.js len=16 kind='decode' n=100000                  ***     57.54 %       ±3.19%  ±4.27%  ±5.61%
webstreams/encoding-streams.js len=16 kind='encode' n=100000                  ***     44.84 %       ±2.38%  ±3.17%  ±4.15%
webstreams/from.js kind='async' n=1000000                                     ***     32.60 %       ±1.34%  ±1.79%  ±2.35%
webstreams/from.js kind='sync' n=1000000                                      ***     39.66 %       ±1.41%  ±1.88%  ±2.44%
webstreams/js_transfer.js n=10000 payload='ReadableStream'                    ***     10.98 %       ±1.56%  ±2.08%  ±2.72%
webstreams/js_transfer.js n=10000 payload='TransformStream'                   ***     12.90 %       ±0.88%  ±1.18%  ±1.53%
webstreams/js_transfer.js n=10000 payload='WritableStream'                    ***     11.77 %       ±0.96%  ±1.28%  ±1.67%
webstreams/lifecycle.js kind='pipe-through' n=50000                           ***     96.41 %       ±3.41%  ±4.58%  ±6.03%
webstreams/lifecycle.js kind='pipe-to' n=50000                                ***     80.15 %       ±7.47% ±10.02% ±13.18%
webstreams/lifecycle.js kind='readable' n=50000                               ***     80.04 %       ±3.10%  ±4.15%  ±5.45%
webstreams/pipe-through.js kind='default' n=500000                            ***     91.16 %       ±2.56%  ±3.43%  ±4.52%
webstreams/pipe-through.js kind='transform' n=500000                          ***     93.68 %       ±3.12%  ±4.19%  ±5.53%
webstreams/pipe-to.js highWaterMarkW=1 highWaterMarkR=1 n=500000              ***    110.48 %       ±2.91%  ±3.89%  ±5.11%
webstreams/pipe-to.js highWaterMarkW=1 highWaterMarkR=1024 n=500000           ***    105.83 %       ±3.89%  ±5.22%  ±6.89%
webstreams/pipe-to.js highWaterMarkW=1 highWaterMarkR=4096 n=500000           ***    109.78 %       ±2.47%  ±3.30%  ±4.33%
webstreams/pipe-to.js highWaterMarkW=1024 highWaterMarkR=1 n=500000           ***    110.77 %       ±2.07%  ±2.78%  ±3.64%
webstreams/pipe-to.js highWaterMarkW=1024 highWaterMarkR=1024 n=500000        ***    109.64 %       ±2.43%  ±3.26%  ±4.30%
webstreams/pipe-to.js highWaterMarkW=1024 highWaterMarkR=4096 n=500000        ***    111.70 %       ±2.52%  ±3.38%  ±4.46%
webstreams/pipe-to.js highWaterMarkW=4096 highWaterMarkR=1 n=500000           ***    110.87 %       ±2.50%  ±3.34%  ±4.37%
webstreams/pipe-to.js highWaterMarkW=4096 highWaterMarkR=1024 n=500000        ***    108.40 %       ±2.36%  ±3.15%  ±4.13%
webstreams/pipe-to.js highWaterMarkW=4096 highWaterMarkR=4096 n=500000        ***    109.79 %       ±2.49%  ±3.32%  ±4.36%
webstreams/readable-async-iterator.js type='bytes' n=100000                   ***     12.19 %       ±2.06%  ±2.74%  ±3.57%
webstreams/readable-async-iterator.js type='normal' n=100000                  ***     15.03 %       ±4.79%  ±6.37%  ±8.30%
webstreams/readable-read-buffered.js bufferSize=1 n=100000                    ***     22.05 %       ±5.25%  ±6.99%  ±9.10%
webstreams/readable-read-buffered.js bufferSize=10 n=100000                   ***     19.89 %       ±3.04%  ±4.04%  ±5.26%
webstreams/readable-read-buffered.js bufferSize=100 n=100000                  ***     27.79 %       ±5.78%  ±7.70% ±10.04%
webstreams/readable-read-buffered.js bufferSize=1000 n=100000                 ***     25.51 %       ±5.83%  ±7.76% ±10.11%
webstreams/readable-read.js type='byob' n=100000                              ***      5.82 %       ±1.45%  ±1.93%  ±2.51%
webstreams/readable-read.js type='normal' n=100000                            ***     34.63 %       ±4.79%  ±6.38%  ±8.31%
webstreams/tee.js type='bytes' n=100000                                       ***     13.65 %       ±1.49%  ±1.98%  ±2.58%
webstreams/tee.js type='normal' n=100000                                      ***     15.97 %       ±2.70%  ±3.59%  ±4.68%

Validated with the full webstreams test suite, WPT streams/compression/encoding, and two differential stress harnesses (adapter scenarios and transform parked-write error/abort/terminate/reentrancy scenarios) whose observable event logs are byte-identical to the previous implementation.

Other lib/ modules use the same __proto__: null literal pattern on hot paths; I'll follow up separately after auditing them.

[nodejs-github-bot]

Review requested:

• @nodejs/performance

[codecov]

Codecov Report

❌ Patch coverage is 96.85039% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.07%. Comparing base (7aaf9b4) to head (36d534f).
⚠️ Report is 59 commits behind head on main.

Files with missing lines	Patch %	Lines
lib/internal/webstreams/transformstream.js	93.65%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #65625      +/-   ##
==========================================
- Coverage   90.13%   90.07%   -0.07%     
==========================================
  Files         751      751              
  Lines      253639   255020    +1381     
  Branches    47790    48157     +367     
==========================================
+ Hits       228618   229703    +1085     
- Misses      16264    16482     +218     
- Partials     8757     8835      +78     

Files with missing lines	Coverage Δ
lib/internal/webstreams/readablestream.js	87.24% <100.00%> (+0.03%)	⬆️
lib/internal/webstreams/writablestream.js	93.79% <100.00%> (+0.30%)	⬆️
lib/internal/webstreams/transformstream.js	93.68% <93.65%> (-0.29%)	⬇️

... and 86 files with indirect coverage changes

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