fix(pandas v3): support pandas v3 by enforcing millisecond timestamp precision

[haakonvt]

No description provided.

[gemini-code-assist]

Code Review

This pull request standardizes the to_pandas export behavior across the SDK to use millisecond precision (datetime64[ms]) for timestamp and datetime columns, aligning with the Cognite API and ensuring compatibility with pandas v3. To eliminate duplicate conversion logic, CogniteResource.to_pandas now delegates to its corresponding list class via a new _LIST_CLASS class variable, with a fallback helper for resource types without a list counterpart. Custom to_pandas overrides (such as in Group and Instances) have been simplified or removed in favor of this unified delegation pattern, and meta-tests have been added to enforce the back-references between resource and list classes. No review comments were provided, so there is no feedback to assess.

[codecov]

Codecov Report

❌ Patch coverage is 99.16318% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 93.69%. Comparing base (8b99b98) to head (cf6d97b).

Files with missing lines	Patch %	Lines
cognite/client/utils/_pandas_helpers.py	90.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2724      +/-   ##
==========================================
- Coverage   93.71%   93.69%   -0.03%     
==========================================
  Files         504      504              
  Lines       51294    51476     +182     
==========================================
+ Hits        48070    48229     +159     
- Misses       3224     3247      +23     

Files with missing lines	Coverage Δ
cognite/client/data_classes/_base.py	93.70% <100.00%> (-0.07%)	⬇️
cognite/client/data_classes/agents/agent_tools.py	98.67% <100.00%> (+0.01%)	⬆️
cognite/client/data_classes/agents/agents.py	100.00% <100.00%> (ø)
cognite/client/data_classes/agents/chat.py	97.11% <100.00%> (+0.01%)	⬆️
cognite/client/data_classes/aggregations.py	89.32% <100.00%> (+0.04%)	⬆️
cognite/client/data_classes/annotations.py	97.89% <100.00%> (+0.04%)	⬆️
cognite/client/data_classes/assets.py	94.47% <100.00%> (+0.02%)	⬆️
cognite/client/data_classes/capabilities.py	97.01% <100.00%> (+<0.01%)	⬆️
cognite/client/data_classes/contextualization.py	91.24% <100.00%> (+0.05%)	⬆️
...te/client/data_classes/data_modeling/containers.py	97.70% <100.00%> (+0.01%)	⬆️
... and 59 more

... and 4 files with indirect coverage changes

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