Allow pdb to be used in pytest

[je-cook]

Description

CliRunner catches all errors by default. Now it only catches sys exit. This means that --pdb now works as expected for pytest args -s still doesnt function the same but now we return the result object which has captured stdout and stderror on it. This doesnt effect capsys etc as they already accomodate that.

Checklist

I confirm that I have completed the following checks:

• My changes follow the PROCESS style guide
• I have justified any large differences in the regression tests caused by this pull request in the comments.
• I have added new tests where appropriate for the changes I have made.
• If I have had to change any existing unit or integration tests, I have justified this change in the pull request comments.
• If I have made documentation changes, I have checked they render correctly.
• I have added documentation for my change, if appropriate.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 49.88%. Comparing base (bd5e644) to head (7c12933).
⚠️ Report is 6 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4578      +/-   ##
==========================================
+ Coverage   49.85%   49.88%   +0.03%     
==========================================
  Files         151      151              
  Lines       29875    29871       -4     
==========================================
+ Hits        14894    14901       +7     
+ Misses      14981    14970      -11     

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