fix: keep access logs when the request peer is gone

[vinismarques]

Closes #34.

json_logging 1.5.1 dereferences Starlette's optional Request.client unguarded, so any request whose peer socket is already gone (kubelet resetting a timed-out readiness probe) loses its access-log line to a formatter traceback on stderr.

The issue suggested passing a custom extractor to init_request_instrument, but that function has no such parameter: the extractor class comes from json_logging's framework registry and is frozen into the RequestUtil singleton by init_fastapi. So request_logging.py subclasses FastAPIRequestInfoExtractor and re-registers it via register_framework_support, called immediately before init_fastapi. Once upstream ships bobbui/json-logging-python#116 the module can be deleted.

Dropping init_request_instrument (the issue's other option) was rejected: it removes every access log, a larger behaviour change than the bug, and an upstream release would not undo it.

Covered by unit tests on both accessors and the registry swap, plus a subprocess test that drives /health with scope["client"] = None and asserts no logging error on stderr; it fails without the fix. Subprocess because json_logging.init_* mutates process-wide logging state irreversibly.