Add regex-based extension filtering using environment variable

[github-actions]

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I implemented a new feature to filter entry points based on their module names using regular expressions. The filter pattern can be specified through the environment variable GIT_BOB_EXTENSIONS_FILTER_REGEXP. By default, all modules are accepted using the pattern ".*". This change affects both the init_prompt_handlers and init_triggers functions in _terminal.py, allowing users to selectively load only the extensions they need by specifying a regex pattern. The implementation is minimal and maintains backward compatibility while adding this new filtering capability.

• src/git_bob/_terminal.py Added regex-based module filtering using GIT_BOB_EXTENSIONS_FILTER_REGEXP environment variable.

closes #540

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 59.00%. Comparing base (ec0f98a) to head (835f9ff).
Report is 4 commits behind head on main.

Additional details and impacted files

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##             main     #541   +/-   ##
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  Coverage   59.00%   59.00%           
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  Files          14       14           
  Lines        1815     1815           
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  Hits         1071     1071           
  Misses        744      744           

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