GeezerVison

Fixes #785

create_connection(sock=) and create_unix_connection(sock=) attached the passed socket to the transport only after await waiter. If the peer resets the connection before the TLS ClientHello is written, connection_lost() closes the transport before the coroutine resumes. The socket was then never detached: it kept the closed fd number and closed it again when garbage-collected, possibly closing an unrelated connection that reused the fd.

This PR attaches the socket right after tr._open(), so every close path detaches it, as on the success path. The existing sock.detach() in the except branch is unchanged; if the socket is already detached, it returns -1.

The same bug happens without TLS when the protocol aborts the transport in connection_made(): create_connection(sock=) then returns normally, but the socket keeps the closed fd number.

Tests:

• test_create_connection_sock_abort_detaches (tests/test_tcp.py) and test_create_unix_connection_sock_abort_detaches (tests/test_unix.py): the protocol calls transport.abort() in connection_made().
• test_create_connection_ssl_sock_reset_detaches (tests/test_tcp.py): the server resets the connection with SO_LINGER 0, and the client calls create_connection(sock=, ssl=) after the RST has arrived.
• test_create_unix_connection_ssl_sock_closed_detaches (tests/test_unix.py): the same for a Unix socket, where the ClientHello write fails with EPIPE.

All tests check sock.fileno() == -1 and run for uvloop and asyncio. On master the uvloop variants fail with 13 != -1 on Linux. With this change they pass (also with PYTHONASYNCIODEBUG=1), and the full test suite passes (python:3.12-slim, 535 tests).

AI disclosure: the fix and tests were made with AI assistance (Claude). I ran them as described above.