gh-155305: Preserve user-provided sockets on transport errors

[RealBhupesh]

Fixes #155305.

Summary:

• Keep caller-owned sockets open when transport creation fails.
• Preserve cleanup for internally created sockets and accepted connections.

Tests:

• ./python.exe -m test test_asyncio.test_base_events test_asyncio.test_events test_asyncio.test_unix_events (500 tests, 3 skipped)

• Issue: asyncio.loop.create_connection closes user-provided socket on transport creation failure (Regression in 3.14.7) #155305

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[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Restore caller sockets' blocking mode on failure

When a caller supplies a blocking socket and protocol_factory() or transport construction raises, this branch now leaves the socket open even though _create_connection_transport() has already changed it to nonblocking at line 1226 (and create_unix_connection() does so before calling this helper). Because no transport was created and ownership remains with the caller, subsequent ordinary socket operations can unexpectedly raise BlockingIOError; preserve and restore the socket's original timeout/blocking state on this failure path.

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