Fix Custom Excepthook

[mxkpp]

This fixed 2 issues with the custom excepthook, which is one of the exit-handling methods applied to ensure certain "cleanup" behavior in various exit situations:

1. There was a typo where sys.excepthook assignment was typed sys.exepthook, so the excepthook was not actually being overridden with a custom method. This typo was masked by how the forcing engine's own err handler was catching exceptions itself and calling sys.exit(1) (triggering the same intended cleanup routine, but for a different exit condition) before the exception bubbled up to the actual Python system excepthook. This typo has been fixed.
2. The custom excepthook was calling the bare sys.__excepthook__ before calling its custom behavior. The intent here was to perform regular excepthook behavior before the cleanup. However as @idtodd pointed out, this means that if other parts of the program had already reassigned sys.excepthook to a custom callable, then that would not be honored. Instead, this PR changes the forcing engine's custom excepthook to save a copy of sys.excepthook (rather than sys.__excepthook__) to be called later before adding its cleanup steps to the final hook. This essentially extends any existing custom excepthook behavior.
3. An improvement was added to err_handler.err_out_screen and err_handler.err_out_screen_para to handle cases of a None message being passed as the err_msg argument.

Additions

Removals

Changes

• Fixed setting of custom excepthook

Testing

1. I watched behavior in the Python debugger.

Screenshots

Notes

Todos

Checklist

• PR has an informative and human-readable title
• Changes are limited to a single goal (no scope creep)
• Code can be automatically merged (no conflicts)
• Code follows project standards (link if applicable)
• Passes all existing automated tests
• Any change in functionality is tested
• New functions are documented (with a description, list of inputs, and expected output)
• Placeholder code is flagged / future todos are captured in comments
• Visually tested in supported browsers and devices (see checklist below 👇)
• Project documentation has been updated (including the "Unreleased" section of the CHANGELOG)
• Reviewers requested with the Reviewers tool ➡️

Testing checklist

Target Environment support

• Linux

[mxkpp]

@idtodd if you could please review this, I would like to push one more improvement to the err_handler.py type-checking before we merge though.

[mxkpp]

@idtodd if you could please review this, I would like to push one more improvement to the err_handler.py type-checking before we merge though.

I've added the improved type checking on the error message handling. I believe this is ready to merge afte review.