[PR #10971/1ee187c0 backport][3.12] Fix WebSocketResponse.prepared not correctly reflect the WebSocket's prepared state

[patchback]

This is a backport of PR #10971 as merged into master (1ee187c).

This PR fixes an issue where the WebSocketResponse.prepared property did not correctly reflect the WebSocket's prepared state, particularly during timeout scenarios.

Previously, the prepared property inherited from StreamResponse only checked for _payload_writer, but in WebSocket timeout scenarios, the _writer could be set while _payload_writer remained None, leading to incorrect state reporting.

Changes

• Added an explicit prepared property to WebSocketResponse that checks for _writer instead of relying on the parent class's _payload_writer check
• Added a check in the prepare() method to prevent double preparation when _writer is already set
• Added comprehensive tests covering timeout scenarios and edge cases where WebSocket state needs to be correctly tracked

fixes #6009

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.16%. Comparing base (bfe0bd1) to head (c283fcb).
Report is 1 commits behind head on 3.12.

✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##             3.12   #10983      +/-   ##
==========================================
+ Coverage   97.88%   98.16%   +0.28%     
==========================================
  Files         130      130              
  Lines       39755    39819      +64     
  Branches     2241     2241              
==========================================
+ Hits        38914    39090     +176     
+ Misses        659      557     -102     
+ Partials      182      172      -10     

Flag	Coverage Δ
CI-GHA	98.05% <100.00%> (+0.26%)	⬆️
OS-Linux	97.78% <100.00%> (+0.01%)	⬆️
OS-Windows	95.27% <100.00%> (?)
OS-macOS	96.95% <100.00%> (+<0.01%)	⬆️
Py-3.10.11	96.84% <100.00%> (+0.27%)	⬆️
Py-3.10.17	97.38% <100.00%> (+0.01%)	⬆️
Py-3.11.12	97.48% <100.00%> (+0.66%)	⬆️
Py-3.11.9	96.93% <100.00%> (+0.27%)	⬆️
Py-3.12.10	97.83% <100.00%> (+0.25%)	⬆️
Py-3.13.3	97.83% <100.00%> (+0.87%)	⬆️
Py-3.9.13	96.73% <100.00%> (+0.27%)	⬆️
Py-3.9.22	97.25% <100.00%> (+0.61%)	⬆️
Py-pypy7.3.16	85.78% <100.00%> (?)
VM-macos	96.95% <100.00%> (+<0.01%)	⬆️
VM-ubuntu	97.78% <100.00%> (+0.01%)	⬆️
VM-windows	95.27% <100.00%> (?)

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[codspeed-hq]

CodSpeed Performance Report

Merging #10983 will not alter performance

_{Comparing patchback/backports/3.12/1ee187c08c9bb59acb53e1c80a06c79a4183de10/pr-10971 (c283fcb) with 3.12 (bfe0bd1)}

Summary

✅ 59 untouched benchmarks