feat: introduce folio abstraction

[mtth]

This change also makes bot edits fully concurrent with both the working tree and index. All changes are applied to an independent tree, committed separately from the current HEAD.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 89.06883% with 27 lines in your changes missing coverage. Please review.

Project coverage is 90.02%. Comparing base (5a46298) to head (7580e61).

Files with missing lines	Patch %	Lines
src/git_draft/toolbox.py	83.33%	10 Missing and 5 partials ⚠️
src/git_draft/drafter.py	91.37%	7 Missing and 3 partials ⚠️
src/git_draft/git.py	94.73%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #67      +/-   ##
==========================================
- Coverage   92.07%   90.02%   -2.05%     
==========================================
  Files          10       10              
  Lines         656      702      +46     
  Branches       46       55       +9     
==========================================
+ Hits          604      632      +28     
- Misses         33       49      +16     
- Partials       19       21       +2     

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