Add Rust, PyO3, and Maturin chapter (book, example, slides, instructor notes)

[thewtex]

Summary

Adds a complete Rust, PyO3, and Maturin chapter to the SIMPLE-Py workshop — a
new book chapter, a runnable PyO3 example project, a Marp slide deck, and a set of
instructor-facing research notes. This fills the "Maturin, PyO3, and Rust" slot that
previously existed only as an empty heading in the Compiled section, giving the
workshop a first-class Rust track alongside its C++ material.

Why

The Compiled section covered pybind11/nanobind (C++) but left Rust as a stub. Rust +
PyO3 + maturin is now a mainstream way to ship compiled Python extensions, so the
workshop needed a self-contained, teachable chapter that mirrors the book's
existing "install-and-lock with pixi" approach and requires no rustup or system Rust.

What's included

Book chapter — content/compiled/04_rust_pyo3.md (wired into myst.yml TOC and
cross-linked from content/compiled/02_binding.md). Walks from motivation through a
first extension to shipping wheels: Why Rust → the toolchain stack → pixi setup → a
first extension → build/iterate loop → benchmarking → classes → native-feeling errors
→ the GIL and free-threading → shipping wheels → exercises → where to go next.

Runnable example — examples/2_04_rust_pyo3/, a minimal pixi-managed PyO3
extension. src/lib.rs exposes a GIL-releasing count_primes, a Point #[pyclass],
a sum_as_string function, and a checked_div that raises a Python exception; with
a pytest suite (tests/) and a pure-Python-vs-Rust benchmark (bench.py). Everything
— the Rust compiler, maturin, Python, pytest — installs from conda-forge via pixi, and
pixi run test / pixi run bench chain a build in front so they never run against a
stale extension.

Slide deck — slides/2_04_rust_pyo3.md, a Marp deck (theme: simplepy) tracking
the chapter for live presentation.

Instructor notes — instructor-notes/: four research notes (PyO3 current state,
maturin workflows, the pixi/conda-forge Rust toolchain, and the Rust-for-Pythonistas
landscape) plus a synthesis deep-dive with a 30-minute teaching runbook. These carry
Obsidian-style frontmatter and [[wiki-links]] and are deliberately kept out of the
myst.yml TOC, so they are never published into the book.

Supporting changes

• AGENTS.md — documents the new examples/ and instructor-notes/ directories and
  scopes the "content, not code" note to the book itself (the example is runnable).
• .pre-commit-config.yaml — excludes the pixi-generated pixi.lock from prettier
  (consistent with its linguist-generated marking in .gitattributes).
• .gitignore — ignores agent-local .serena/ tool state.

Notes for reviewers

• All prose is em-dash/en-dash free (ASCII punctuation throughout); the branch history
  was rewritten so no commit diff introduces those characters.
• Instructor-note technical claims were fact-checked against primary sources (PyO3 0.29
  docs, maturin 1.14.1 CLI output, the conda-forge rust feedstock, PEP 803) and passed a
  CodeRabbit review; the benchmark timings were captured from a real pixi run bench.
• prek (all hooks) passes and bun run build-book / build-slides both build cleanly.

🤖 Generated with Claude Code

[thewtex]

Superseded by the upstream PR against scikit-build/SIMPLE-Py: scikit-build#32 (branch rebased onto current upstream main; chapter folded into the existing 03_rust.md stub).