Test gaps: aiohttp paths, privacy claim, self-instrumentation, 5xx retry

[AndresL230]

Summary

Four explicit claims in the README have no test coverage:

• aiohttp interceptor branch. _interceptor.py patches aiohttp.ClientSession._request, but tests/test_interceptor.py only covers urllib3, httpx sync, and httpx async. Zero direct aiohttp tests.
• No headers/bodies captured (privacy contract). Add a test that asserts RawEvent-shaped output carries no dict-typed payload field, plus a test that issues a request with sensitive headers and confirms they don't surface.
• No self-instrumentation. Verify that urllib.request calls made from _post_cloud do not trigger the urllib3 patch.
• 5xx retry path. test_no_retry_on_4xx exists but no positive test that max_retries actually runs n attempts with exponential backoff.

Also missing:

• deprecation-warning test for flush_interval
• would_overflow early-flush path test
• handle.dispose() actually stops new flushes
• _LocalTransport graceful no-op when websockets missing
• Flask graceful degradation when flask is missing

Fix

Add tests for each. The aiohttp tests should mirror the existing httpx async tests (success, 4xx capture, latency, response-bytes, double-count guard via reentrancy).

Files

• tests/test_interceptor.py
• tests/test_transport.py
• tests/test_init.py
• tests/test_flask.py

Priority

P1 — the most-marketed claims (privacy, no self-trace) are unverified; an entire interceptor branch (aiohttp) is untested.