WSTransport.close() scheduled ws.close(code=1011) on every call, so
handle_ws's normal teardown reported 1011 before its own close. Move the
off-loop socket close into a one-shot WSTransport.abort() that the fanout
overflow path calls; close() is byte-identical to main again. Rename
_close_stalled_socket -> _close_socket(code, reason) with accurate log
text, share an _on_loop() helper with write(), and make the overflow test's
slow peer a real WSTransport whose socket close must be awaited with 1011.
Co-authored-by: KoNit-K <konit.block@protonmail.com>
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