Replace add_reader/add_writer with async socket ops for Windows compatibility

[Copilot]

UDPTransport used loop.add_reader()/add_writer() which are not supported on Windows' ProactorEventLoop.

Changes

• RX path: Replace add_reader callbacks with asyncio.Task loops using loop.sock_recvfrom() (Python 3.11+). Tasks tracked in _unicast_rx_tasks and _mcast_rx_tasks for lifecycle management.
• TX path: Replace manual add_writer/remove_writer writability-wait in _async_sendto with loop.sock_sendto().
• Cleanup: close() and _UDPSubjectListener.close() cancel tasks instead of calling remove_reader().
• Tests: Remove _SKIP_WINDOWS marker from all integration test classes.

Before:

# Event-driven (SelectorEventLoop only)
self._loop.add_reader(sock.fileno(), self._on_unicast_data, i)

After:

# Cross-platform async task
task = self._loop.create_task(self._unicast_rx_loop(sock, i))
self._unicast_rx_tasks.append(task)

Added asyncio.sleep(0.1) backoff in RX loops on persistent OSError to avoid tight-looping (the old add_reader approach was inherently event-gated).

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• 239.0.0.10
  • Triggering command: REDACTED, pid is -1 (packet block)
• 239.0.0.100
  • Triggering command: REDACTED, pid is -1 (packet block)
• 239.0.0.42
  • Triggering command: REDACTED, pid is -1 (packet block)
• 239.0.0.50
  • Triggering command: REDACTED, pid is -1 (packet block)
• 239.0.0.55
  • Triggering command: REDACTED, pid is -1 (packet block)
• 239.0.0.60
  • Triggering command: REDACTED, pid is -1 (packet block)
• 239.0.0.7
  • Triggering command: REDACTED, pid is -1 (packet block)
• 239.0.0.70
  • Triggering command: REDACTED, pid is -1 (packet block)
• 239.0.0.80
  • Triggering command: REDACTED, pid is -1 (packet block)
• 239.0.0.99
  • Triggering command: REDACTED, pid is -1 (packet block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

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