fix(tokio-quiche): wake idle listener when accept stream is dropped

[codeandsolder]

Summary

Wake an idle tokio-quiche router when its accept stream is dropped so the listener socket/address is released promptly.

Problem

The router checks accept_sink.is_closed() when it is polled, but an otherwise idle router does not register a wakeup tied to the receiver being dropped. Dropping the accept stream can therefore leave the router task asleep while still holding the UDP socket, delaying teardown/rebind indefinitely until unrelated activity wakes it.

Change

Poll a cloned sender's closed() future alongside the router's normal work. That gives the task a wake source tied directly to receiver shutdown without changing the success path.

A regression test binds a listener, drops the accept-side streams while it is idle, and verifies the same address can be rebound promptly.

The shared Rust 1.98.1 validation run passed idle_listener_releases_socket_after_stream_drop; repository nightly formatting is clean.

[ghedo]

Closing as a duplicate of #2763. Both use the same receiver-closed future to wake an idle listener when the accept stream is dropped, with equivalent teardown regression coverage.