Close connection when TimeoutConnection wrapping fails

[Seanstoppable]

This PR was generated with the assistance of GitHub Copilot CLI and may require human review.

Problem

In Dialer.DialContext (conn.go), if NewTimeoutConnection returns an error after the underlying connection has already been established, the function returns the error without closing the connection — leaking the established socket.

Fix

Close the connection on the error path before returning.

ret, err := NewTimeoutConnection(ctx, conn, ...)
if err != nil {
    _ = conn.Close() // avoid leaking the established connection
    return nil, err
}

Severity: low. Found via AI code review.