feat/preserver maildir subdirectories

[SvenRohrTNG]

Resolves #156

Hi @michaeladler ,

please triple check, since I am new to rust ;-)
Has been running successfully on my local machine for the last hour or so :-)

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 3 lines in your changes missing coverage. Please review.

Project coverage is 62.15%. Comparing base (8a5b8b0) to head (d887b62).
Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
src/lib/action.rs	0.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #163      +/-   ##
==========================================
- Coverage   62.40%   62.15%   -0.25%     
==========================================
  Files           6        6              
  Lines         508      510       +2     
==========================================
  Hits          317      317              
- Misses        191      193       +2     

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[michaeladler]

Thanks for your contribution!