Improve mypy config; remove typing casts

[jwodder]

No description provided.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (744de47) 75.90% compared to head (bedbc6e) 75.99%.
Report is 12 commits behind head on draft.

Additional details and impacted files

@@            Coverage Diff             @@
##            draft     #369      +/-   ##
==========================================
+ Coverage   75.90%   75.99%   +0.09%     
==========================================
  Files          14       14              
  Lines        2548     2558      +10     
  Branches      568      568              
==========================================
+ Hits         1934     1944      +10     
  Misses        451      451              
  Partials      163      163              

Files	Coverage Δ
tools/backups2datalad/adandi.py	81.49% <100.00%> (+0.67%)	⬆️
tools/backups2datalad/adataset.py	78.73% <100.00%> (+0.14%)	⬆️
tools/backups2datalad/zarr.py	73.55% <100.00%> (ø)

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