Fix GH-23879: Do not report AcceptFailed on non-blocking accept timeout

[lazerg]

On a non-blocking listener, stream_socket_accept() with no client waiting went down the same path as a real failure and raised AcceptFailed ("Connection timed out"). That makes the usual "accept until empty" drain loop throw in StreamErrorMode::Exception, and the only way to tell it apart from something like fd exhaustion was the message text.

The TCP and TLS transports now treat a poll timeout or EAGAIN on a non-blocking listener as "nothing to accept" and return success without a client, so stream_socket_accept() returns false without reporting an error. Blocking listeners still report the timeout as before. PHP_TIMEOUT_ERROR_VALUE moved from network.c to php_network.h so the transports can check for it.

Fixes #23879