stop() on a listen event does not stop accepting #305

libuv_listen_stop (libuv_reactor.c) only zeroes loop_ref_count and decrements the event count: libuv has no call that undoes uv_listen (checked in libuv v1.52.1: uv__tcp_listen starts the POLLIN watcher, and uv_read_stop is a no-op on a listening handle because UV_HANDLE_READING is never set). A stopped listen event therefore keeps accepting, and every connection reaches its callbacks.

Consumer impact: true-async-server pauses its listeners at its connection cap so that new connections wait in the kernel backlog; instead each one is accepted and answered 503 by the server's safety net. Reproduced 5 of 5 by the server's tests/phpt/server/h1/062-h1-paused-listener-leaves-the-backlog.phpt.

Fix (reviewed by a Critic and a Sage before code): pause by leaving the connection unaccepted. On Unix libuv then stops watching the socket itself (unix/stream.c:528-531) and restarts on the next successful uv_accept; on Windows a completed AcceptEx stays pending and is not re-posted. The first start() runs uv_listen; a later one unpauses and delivers the held connection on the next loop tick. A uv_poll accept loop was rejected: several polls on one socket busy-loop on Windows, EMFILE would spin, and named pipes cannot be polled.