Add basic CLI

[gerlero]

As discussed with @HenningScheufler.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 51 lines in your changes missing coverage. Please review.

Project coverage is 85.28%. Comparing base (5076034) to head (a3fda5b).
Report is 73 commits behind head on main.

Files with missing lines	Patch %	Lines
foamlib/__main__.py	0.00%	37 Missing ⚠️
foamlib/_util.py	0.00%	14 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #349      +/-   ##
==========================================
- Coverage   88.20%   85.28%   -2.92%     
==========================================
  Files          15       17       +2     
  Lines        1492     1543      +51     
==========================================
  Hits         1316     1316              
- Misses        176      227      +51     

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[gerlero]

@HenningScheufler I'm not sure if case directories should be passed as arguments or options (i.e. with --case). Having them as arguments looks cleaner (e.g. foamlib run /path/to/case), while having them as options allows for adding other arguments to run (e.g. foamlib run blockMesh --case /path/to/case). Let me know if you have any opinions on this.

Whatever the choice, plain foamlib run without any arguments/options should run the case in the current working directory.

[HenningScheufler]

We may want support additional options to run cases. So i think the --cases is a good option.