DM-2412 fix aggregate property casing + add files tests cleanup

[haakonvt]

Raised on slack: https://cognitedata.slack.com/archives/CG10VQPFX/p1733302661860609

1. fix aggregate property casing
2. add files tests cleanup
3. fix wrong type annotations for aggregate_cardinality_properties

[codecov]

Codecov Report

Attention: Patch coverage is 80.00000% with 1 line in your changes missing coverage. Please review.

Project coverage is 90.49%. Comparing base (279cda9) to head (106ce42).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
cognite/client/_api_client.py	75.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2059      +/-   ##
==========================================
- Coverage   90.49%   90.49%   -0.01%     
==========================================
  Files         141      141              
  Lines       22483    22483              
==========================================
- Hits        20346    20345       -1     
- Misses       2137     2138       +1     

Files with missing lines	Coverage Δ
cognite/client/_api/documents.py	77.11% <ø> (ø)
cognite/client/_version.py	100.00% <100.00%> (ø)
cognite/client/_api_client.py	90.34% <75.00%> (+0.16%)	⬆️

... and 1 file with indirect coverage changes

[vvb16]

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