Fix Windows portability failures in the pre-1 artifact suite

[RobLe3]

Summary

• keep the node accept lifecycle on the asyncio loop so cancellation does not leave a blocking executor thread on Windows
• route HTTP-only listeners directly to the HTTP server instead of applying experimental native-frame socket peeking
• use non-destructive Windows process liveness checks and platform-correct trust-store mode semantics
• make affected fixtures, subprocess teardown, UTF-8 reads and service tests portable on Windows

Evidence

• AWS Windows x86-64 v8 diagnostic attempts reached bootstrap, preflight and the Python artifact builder; the final retained diagnostic reduced the failure set to relay HTTP polling, proxy E2E teardown and one POSIX-only trust-store assertion
• python3 scripts/run_sdk_quality.py --output /tmp/iicp-python-quality-windows-fixes.json
  • CPython 3.11, 3.12 and 3.13: 1,256 passed, 2 skipped, 9 subtests each
  • coverage: 76.08% (minimum 75%)
  • Ruff, mypy no-regression baseline, dependency audit, locked build and clean wheel install passed
• CPython 3.14 full suite: 1,256 passed, 2 skipped, 9 subtests
• the 39 affected relay/multiplexer/trust/proxy tests passed in ten consecutive local repetitions

This is source-level remediation from a diagnostic run. It grants no Windows artifact or qualification credit; one later clean, source-bound Windows run remains required.

Refs #119