fix(boto3): Fix botocore SigV4 failures caused by post-sign trace propagation

[pabloDeputter]

WIP!

Description

• merge Sentry baggage with existing vendor (e.g. Datadog) baggage in botocore'sbefore-sign hook; avoiding post-sign header tampering that invalidates the SigV4 signature.
• Skip propagation for presigned requests

Issues

Resolves: #7031 & PY-2667

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 📊

✅ 96711 passed | ❌ 1 failed | ⏭️ 6191 skipped | Total: 102903 | Pass Rate: 93.98% | Execution Time: 348m 30s

📊 Comparison with Base Branch

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

➕ New Tests (1)

View new tests

• test_continuous_profiler_auto_start_and_stop_sampled_span_streaming[non-experiment-thread]
  • File: tests.profiler.test_continuous_profiler
  • Status: ❌ Failing

❌ Failed Tests

test_continuous_profiler_auto_start_and_stop_sampled_span_streaming[non-experiment-thread]

File: tests.profiler.test_continuous_profiler
Suite: py3.7-common
Error: AssertionError: profiler should not be running assert 'f5dabaf9cc614ef5a7a26765b84e4360' is None + where 'f5dabaf9cc614ef5a7a26765b84e4360' = get_profiler_id()

Stack Trace

tests/profiler/test_continuous_profiler.py:896: in test_continuous_profiler_auto_start_and_stop_sampled_span_streaming
    assert get_profiler_id() is None, "profiler should not be running"
E   AssertionError: profiler should not be running
E   assert 'f5dabaf9cc614ef5a7a26765b84e4360' is None
E    +  where 'f5dabaf9cc614ef5a7a26765b84e4360' = get_profiler_id()

✅ Patch coverage is 81.48%. Project has 2513 uncovered lines.
✅ Project coverage is 89.91%. Comparing base (base) to head (head).

Files with missing lines (2)

File	Patch %	Lines
sentry_sdk/integrations/stdlib.py	80.00%	⚠️ 11 Missing and 4 partials
sentry_sdk/integrations/boto3.py	84.62%	⚠️ 4 Missing and 4 partials

Coverage diff

@@            Coverage Diff             @@
##          main       #PR       +/-##
==========================================
+ Coverage    89.90%    89.91%    +0.01%
==========================================
  Files          193       193         —
  Lines        24822     24896       +74
  Branches      8924      8958       +34
==========================================
+ Hits         22315     22383       +68
- Misses        2507      2513        +6
- Partials      1417      1423        +6

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