Follow-ups on top of the salvaged commits from PR #87111 (@HexLab98) and
PR #87265 (@JoaoMarcos44):
- keep main's #92991 stall watchdog (150s progress-based) as the single
steady-state liveness probe instead of adding a second overlapping one
- orphaned-client aclose() cleanup uses the wall-clock thread deadline and
is tracked in _background_tasks so a wedged close can neither hang nor
leak one task per reconnect attempt (from #87265's review findings)
- merge #87265's no-keepalive getUpdates pool (max_keepalive_connections=0)
with #87111's TCP-keepalive socket options on all transports
- add tests/gateway/test_telegram_closewait_windows_live.py: live probes
against a real half-closing HTTP server, skipif non-win32, wired into
the on-demand windows-venv-e2e lane (wine2e/**)
7790c8f4c4