fix(tracing): Stop setting NoOpSpan on scope in the streaming trace lifecycle

[alexander-alderman-webb]

Description

Do not set a transaction-based span on the scope when span streaming. The early returns in start_span() and start_transaction() are not sufficient as they return NoOpSpan when span streaming, and NoOpSpan still mutates scopes on __enter__() and __exit__().

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

[github-actions]

Codecov Results 📊

✅ 91914 passed | ⏭️ 6302 skipped | Total: 98216 | Pass Rate: 93.58% | Execution Time: 320m 34s

📊 Comparison with Base Branch

Metric	Change
Total Tests	—
Passed Tests	📈 +1
Failed Tests	📉 -1
Skipped Tests	—

➖ Removed Tests (1)

View removed tests

• test_circular_references
  • File: tests.tracing.test_misc

All tests are passing successfully.

✅ Patch coverage is 100.00%. Project has 2485 uncovered lines.
❌ Project coverage is 89.65%. Comparing base (base) to head (head).

Coverage diff

@@            Coverage Diff             @@
##          main       #PR       +/-##
==========================================
- Coverage    89.68%    89.65%    -0.03%
==========================================
  Files          193       193         —
  Lines        24007     24013        +6
  Branches      8342      8346        +4
==========================================
+ Hits         21529     21528        -1
- Misses        2478      2485        +7
- Partials      1387      1387         —

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