Add process termination diagnostic logging in PyGameActivity

[Micha062301]

This change improves diagnostic capabilities by adding exit code logging when a Pygame process terminates. Preserving information about why a process exited will help troubleshoot issues in student code.

The change:

• Adds a dedicated callback function for process termination
• Logs when a pygame process exits with a non-zero exit code
• The addition of logging doesn't change the functional behavior and doesn't impact compatibility.

Tested on Sugar 0.116 with multiple process exit scenarios to ensure proper logging and activity termination behavior.

[quozl]

Thanks, but testing on Sugar 0.116 is unsuitable, please test on Sugar 0.121 or the HEAD of the master branch of Sugar.

[Micha062301]

I've re-tested the changes on Sugar 0.121 and the current HEAD of the master branch. I'm happy to report that all tests passed successfully on both versions:

Normal program exit (code 0): Activity closes normally without logging
Error exit (code 1): Activity closes with appropriate diagnostic logging
Crash scenarios: Activity handles termination properly with logging