Add tests pinning ownership of a stalled WebSocket parser

[aiolibsbot]

What do these changes do?

Add two functional tests that pin the parser-ownership contract #13393 introduces:
ClientWebSocketResponse._parser and WebSocketResponse._parser. Each test feeds one
oversized read, simulates the peer vanishing, collects, and drains.

Targets fix-ws-queue, not master.

Are there changes in behavior for the user?

No, tests only.

Is it a substantial burden for the maintainers to support this?

No. Two tests, no fixtures, no timing dependency — the read and the connection loss are
both driven synchronously.

Related issue number

Follow-up to #13393. Full reference-scope analysis posted as a comment there.

Checklist

• I think the code is well written
• Unit tests for the changes exist
• Documentation reflects the changes — N/A
• If you provide code modification, please add yourself to CONTRIBUTORS.txt — already listed
• Add a new news fragment into the CHANGES/ folder — N/A, covered by CHANGES/13393.bugfix.rst on the base branch (needs bot:chronographer:skip if the bot objects)

Why these tests

The queue reaches the stalled parser through a weak reference, and both protocols drop
their strong reference on connection loss (ResponseHandler.connection_lost and
RequestHandler.connection_lost both feed_eof() then _payload_parser = None). The
two _parser assignments in this PR are the only thing keeping the parked frames
reachable, and nothing failed if they were removed.

Reverting ws_resp._parser = parser in client.py, or the self._parser assignment in
web_ws.py, makes each test report assert 4097 == 8000 — 3903 already-received frames
collected, delivered as a normal CLOSED, no exception anywhere.

Test run

$ PYTHONPATH=. pytest tests/test_websocket_parser.py tests/test_client_ws_functional.py \
    tests/test_web_websocket_functional.py tests/test_web_websocket.py \
    tests/test_client_ws.py tests/test_websocket_handshake.py --numprocesses=auto
336 passed in 5.36s                       # with the _websocket Cython extensions built

$ AIOHTTP_NO_EXTENSIONS=1 PYTHONPATH=. pytest <same>
334 passed, 2 skipped in 4.87s

Cython coverage: aiohttp/_websocket/reader_c and mask were cythonized and compiled
locally (the full make install-dev needs a Node.js build of the vendored llhttp, which
was unavailable). weakref.ref() on the compiled WebSocketReader works with the new
cdef object __weakref__ slot.

Drafted with Claude Opus 5 (Kōan agent); reviewed by @bdraco.

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Quality Report

Changes: 18 files changed, 372 insertions(+), 21 deletions(-)

Code scan: clean

Tests: failed (FAILED)

Branch hygiene: clean

Generated by Kōan