GH-87: Improve DirPathCalc and its relatives

[pydsigner]

Closes #87.

[codecov]

Codecov Report

Attention: 1 lines in your changes are missing coverage. Please review.

Comparison is base (9759662) 78.10% compared to head (d18127d) 78.31%.

Files	Patch %	Lines
src/anchovy/paths.py	91.66%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #88      +/-   ##
==========================================
+ Coverage   78.10%   78.31%   +0.21%     
==========================================
  Files          18       18              
  Lines        1201     1199       -2     
==========================================
+ Hits          938      939       +1     
+ Misses        263      260       -3     

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