MAINT: Bound WebSocket initialization receive time

[Aizen__28 (Yudeeswaran)]

Summary

• Give WebSocket initialization one overall timeout budget across all discarded initial messages using asyncio.timeout.
• Keep initialization receiving on its own budget, separate from normal response receiving and conversation restoration.
• Document the timeout behavior for response_timeout_seconds.
• Add regression coverage showing that individually timely receives still time out when their combined duration exceeds the initialization budget.
• Add cancellation coverage confirming cancellation propagates and the uninitialized connection is closed.

Issue and claim

• Issue: Python 3.11 adoption opportunities: claim one improvement at a time #3166
• Claim: P311-09 — Use scoped operation timeouts with asyncio.timeout

Validation

• Focused test module: 37 passed.
• Ruff check passed for both changed files.
• git diff --check passed.

[hannahwestra25]

couple of test nits:
wait_for_message on line 731 is annotated -> str but never returns — asyncio.Event().wait() isn't NoReturn, so ty flags invalid-return-type and make ty fails in CI. Same fix as wait_forever above it: add return "unreachable".

And the shared-budget test is a bit tight — 0.5s budget with two 0.35s sleeps only tolerates 150ms of overshoot before await_count drops to 1. On loaded CI runners that could flake. Maybe assert a timeout happens and await_count < n instead of an exact count?