ref(openai-agents): Drop support for stream_gen_ai_spans

[alexander-alderman-webb]

Description

Set stream_gen_ai_spans=False to maintain assertions for the static trace lifecycle.
Transaction support will be removed as a follow up.

Issues

Reminders

• Please add tests to validate your changes, and lint your code using uv run ruff.
• Add GH Issue ID & Linear ID (if applicable)
• PR title should use conventional commit style (feat:, fix:, ref:, meta:)
• For external contributors: CONTRIBUTING.md, Sentry SDK development docs, Discord community

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[github-actions]

Codecov Results 📊

✅ 89579 passed | ⏭️ 4164 skipped | Total: 93743 | Pass Rate: 95.56% | Execution Time: 292m 14s

📊 Comparison with Base Branch

Metric	Change
Total Tests	📉 -43952
Passed Tests	📉 -41006
Failed Tests	—
Skipped Tests	📉 -2946

All tests are passing successfully.

✅ Patch coverage is 100.00%. Project has 2271 uncovered lines.
✅ Project coverage is 90.35%. Comparing base (base) to head (head).

Coverage diff

@@            Coverage Diff             @@
##          main       #PR       +/-##
==========================================
+ Coverage    90.27%    90.35%    +0.08%
==========================================
  Files          193       185        -8
  Lines        25715     23539     -2176
  Branches      9502      8636      -866
==========================================
+ Hits         23213     21268     -1945
- Misses        2502      2271      -231
- Partials      1433      1363       -70

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