feat(celery): Support span streaming

[sentrivana]

Description

Support streaming mode in the Celery integration.

This is the first integration that contains explicit guards against creating certain spans as segments, mirroring how start_span works currently -- it won't create a span if there's no transaction. In Celery, there were multiple spots that, if we just replaced all legacy start_spans with the new traces.start_span, would've created new segment spans, leading to a change in behavior.

TODO:

• replace APIs
• map data to attributes from conventions
• run tests in streaming mode

Issues

• Closes Migrate celery to span first #6009
• Closes PY-2311

[linear-code]

PY-2311 Migrate celery to span first

[github-actions]

Semver Impact of This PR

🟡 Minor (new features)

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[github-actions]

Codecov Results 📊

✅ 142 passed | Total: 142 | Pass Rate: 100% | Execution Time: 22.00s

📊 Comparison with Base Branch

Metric	Change
Total Tests	📈 +116
Passed Tests	📈 +116
Failed Tests	—
Skipped Tests	—

All tests are passing successfully.

❌ Patch coverage is 0.00%. Project has 14186 uncovered lines.
✅ Project coverage is 33.71%. Comparing base (base) to head (head).

Files with missing lines (1)

File	Patch %	Lines
__init__.py	3.26%	⚠️ 267 Missing

Coverage diff

@@            Coverage Diff             @@
##          main       #PR       +/-##
==========================================
+ Coverage    27.64%    33.71%    +6.07%
==========================================
  Files          190       190         —
  Lines        21358     21399       +41
  Branches      7066      7096       +30
==========================================
+ Hits          5903      7213     +1310
- Misses       15455     14186     -1269
- Partials       561       700      +139

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