test: preserve coalesced WebSocket deadline frames

[MikiEEE]

Summary

• preserve WebSocket bytes that arrive in the same TCP read as the HTTP 101 handshake
• reuse already-decoded Close events when Ping and Close frames arrive together
• remove the Python 3.10 timing race blocking the v0.1.0 release PR

This is a test-only change; production protocol behavior is unchanged.

Validation

• formerly failing deadline loopback test passed 30 consecutive runs
• full suite passed: 182 tests
• compileall and git diff --check passed