chore: Remove more old transaction stuff

[sentrivana]

• remove scope.transaction (set_transaction_name remains for now; changed all direct uses of scope.transaction = to use set_transaction_name instead)
• remove more interop utils (_serialized_v1_attribute_to_serialized_v2_attribute etc.)
• remove event processor-based transaction name setting (superseded by set_transaction_name directly in patches)
• ...

[github-actions]

Codecov Results 📊

✅ 64517 passed | ❌ 1 failed | ⏭️ 3049 skipped | Total: 67567 | Pass Rate: 95.49% | Execution Time: 183m 45s

📊 Comparison with Base Branch

Metric	Change
Total Tests	📉 -67885
Passed Tests	📉 -63804
Failed Tests	📈 +1
Skipped Tests	📉 -4082

❌ Patch coverage is 58.33%. Project has 2101 uncovered lines.
❌ Project coverage is 90.11%. Comparing base (d68570b) to head (724608f).

Files with missing lines (2)

File	Patch %	Lines
sentry_sdk/integrations/django/init.py	0.00%	⚠️ 4 Missing
sentry_sdk/api.py	0.00%	⚠️ 1 Missing

Coverage diff

@@            Coverage Diff             @@
##        master       #PR       +/-##
==========================================
- Coverage    90.18%    90.11%    -0.07%
==========================================
  Files          193       180       -13
  Lines        25768     21237     -4531
  Branches      9532      7666     -1866
==========================================
+ Hits         23236     19136     -4100
- Misses        2532      2101      -431
- Partials      1432      1211      -221

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