fix(fastapi): Stop eagerly consuming request bodies for streamed spans

[alexander-alderman-webb]

Note: Depends on #6287

Description

Only attach cached request bodies to streamed spans to avoid relying on an eagerly consumed request body. Use the _json and _form attributes instead of json() and form() accessors to ensure that the request body is not consumed by the SDK.

Note: by using _json and _form directly we can no longer distinguish between raw data payloads and payloads that were not cached on the Request object. The attribute is therefore omitted if the request body is not cached, since the endpoint may not have accessed it.

The integration can still cause application hangs if middleware or handlers deprive the receive() callable instead of using Starlette accessors. Reliance on the overly ambitious request body access is only eliminated for streamed spans (and only persists for errors with the change).

• Remove test_request_body_data_does_not_scrub_pii_span_streaming() since test_formdata_request_body() already asserts that fields in the request body are not scrubbed.
• Remove test_request_body_data_annotated_value_top_level_span_streaming() because the attribute is no longer set if the request body is not JSON or FormData.

Issues

Reminders

• Please add tests to validate your changes, and lint your code using tox -e linters.
• 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 📊

✅ 88711 passed | ⏭️ 6013 skipped | Total: 94724 | Pass Rate: 93.65% | Execution Time: 301m 8s

📊 Comparison with Base Branch

Metric	Change
Total Tests	📉 -77
Passed Tests	📉 -65
Failed Tests	—
Skipped Tests	📉 -12

All tests are passing successfully.

✅ Patch coverage is 100.00%. Project has 2365 uncovered lines.
❌ Project coverage is 89.87%. Comparing base (base) to head (head).

Coverage diff

@@            Coverage Diff             @@
##          main       #PR       +/-##
==========================================
- Coverage    89.90%    89.87%    -0.03%
==========================================
  Files          192       192         —
  Lines        23324     23352       +28
  Branches      8020      8024        +4
==========================================
+ Hits         20969     20987       +18
- Misses        2355      2365       +10
- Partials      1327      1326        -1

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[sentrivana]

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