Propagate FastAPI exceptions to framework handlers

[vrslev]

Summary

• Stop converting escaping FastAPI exceptions into blank 500 responses.
• Re-raise them so Starlette/FastAPI exception handlers and automatic Sentry integration receive the original exception.
• Keep normal and handled-response access logging unchanged; escaping exceptions are left to the outer framework error boundary to avoid duplicate Sentry events and inaccurate pre-handler status logging.
• Give every FastStream message its own Sentry isolation scope across the complete subscriber lifecycle, including the built-in critical error log.
• Cover both brokers configured during bootstrap and brokers attached from FastStream startup hooks.
• Do not add HTTPX or HTTPX2 instrumentor configuration; Microbootstrap continues to auto-load both installed OpenTelemetry entry points.

Verification

• Full test suite: 203 passed, 99% coverage.
• FastStream bootstrapper suite: 9 passed; the changed module reached 100% coverage.
• The concurrent-message regression test verifies each automatic FastStream error log sees its own conversation tag and the parent scope remains clean.
• The FastAPI Sentry regression test asserts exactly one exception event with its traceback.
• Ruff format/check passed.
• MyPy passed.
• git diff --check passed.
• GitHub Python 3.10-3.14 matrix: 17 checks passed, 0 failed.

Compatibility

TestClient with raise_server_exceptions=True now propagates unhandled exceptions as Starlette normally does. Production Starlette still renders its configured 500 response, and custom Exception/500 handlers are no longer bypassed.

FastStream message-local Sentry data no longer leaks into concurrent or subsequent messages. Global Sentry scope data remains inherited. The isolation boundary applies to both existing and startup-configured brokers.

Dependency

Front VA-7612 automatic Sentry capture depends on the patch release from this PR; service code does not call capture_exception.

Jira: https://jira.raiffeisen.ru/browse/VA-7612

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

Flag	Coverage Δ
unittests	98.96% <100.00%> (+0.17%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
microbootstrap/bootstrappers/faststream.py	100.00% <100.00%> (ø)
microbootstrap/middlewares/fastapi.py	100.00% <100.00%> (+9.09%)	⬆️

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