chore: implement to_pandas support for raw state (non-array) Datapoints classes

[haakonvt]

Adds support for Datapoints and DatapointsList to_pandas() conversion of raw state datapoints

[gemini-code-assist]

Code Review

This pull request adds support for converting state datapoints to pandas DataFrames, introducing parameters to exclude numeric or string states. Feedback on the changes includes addressing a potential NotImplementedError when converting empty state datapoints to a DataFrame, and removing dead code branches that handle older pandas versions.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.15%. Comparing base (e5be404) to head (4c2afcf).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2810      +/-   ##
==========================================
+ Coverage   93.12%   93.15%   +0.03%     
==========================================
  Files         516      516              
  Lines       53701    53788      +87     
==========================================
+ Hits        50008    50106      +98     
+ Misses       3693     3682      -11     

Files with missing lines	Coverage Δ
cognite/client/data_classes/datapoints.py	90.68% <ø> (ø)
cognite/client/utils/_pandas_helpers.py	93.27% <100.00%> (+0.77%)	⬆️
...ests/tests_integration/test_api/test_datapoints.py	99.35% <100.00%> (+<0.01%)	⬆️
...ts/tests_unit/test_data_classes/test_datapoints.py	100.00% <100.00%> (ø)

... and 5 files with indirect coverage changes

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