test(bigquery): add debug info to socket leak test

[chalmerlowe]

Problem

The system test test_dbapi_connection_does_not_leak_sockets has been failing intermittently with minor socket count discrepancies (e.g., 7 instead of 6). Previous attempts to fix this have not fully eliminated the flakiness, likely due to non-deterministic garbage collection or Operating System cleanup delays. Without knowing the exact state of these "leaked" sockets (e.g., TIME_WAIT vs CLOSE_WAIT), it is difficult to determine if this is a real resource leak in the application or just OS noise.

Solution

This PR wraps the socket count assertion in a try...except AssertionError block. If the assertion fails, it captures the status, local address, and remote address of all active network connections for the current process and appends this information to the failure message.

Notes to Reviewers

• This change does not attempt to fix the underlying flakiness or leak. It is purely diagnostic.
• The detailed socket state will help us distinguish between expected OS delays (TIME_WAIT) and real application leaks (CLOSE_WAIT or ESTABLISHED) in future CI/CD runs.
• This approach avoids running expensive system tests repeatedly to try and capture an intermittent failure manually.

[gemini-code-assist]

Code Review

This pull request adds a try-except block to capture and log detailed socket connection debug information when the test_dbapi_connection_does_not_leak_sockets test fails. The review feedback correctly identifies that current_process.net_connections() is not a valid method and will raise an AttributeError, masking the assertion failure, and suggests using current_process.connections() instead.