feat(state time series): add retrieve_arrays support for raw state datapoints

[haakonvt]

Extends DatapointsArray with numeric_states and string_states and adds support for retrieving (possibly nullable) raw state datapoints using retrieve_arrays (using numpy).

As Gemini is pointing out, some slicing mechanics is missing. This is planned as a separate PR.

[gemini-code-assist]

Code Review

This pull request implements support for retrieving raw state datapoints using retrieve_arrays(...) by handling state datapoints in the underlying numpy unpacking and result generation tasks, and adding numeric_states and string_states attributes to DatapointsArray. The review feedback highlights a critical bug where indexing, slicing, or dumping the retrieved state datapoints will fail or result in data loss due to plural vs singular attribute mismatches (e.g., numeric_states vs numeric_state) and their omission from DatapointsArray._data_fields.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.13%. Comparing base (4c2afcf) to head (08de949).

Additional details and impacted files

@@                           Coverage Diff                            @@
##           add-state-ts-retrieve-support-pandas    #2812      +/-   ##
========================================================================
- Coverage                                 93.15%   93.13%   -0.03%     
========================================================================
  Files                                       516      516              
  Lines                                     53788    53832      +44     
========================================================================
+ Hits                                      50106    50135      +29     
- Misses                                     3682     3697      +15     

Files with missing lines	Coverage Δ
cognite/client/_api/datapoint_tasks.py	95.69% <100.00%> (+0.08%)	⬆️
cognite/client/data_classes/datapoints.py	90.58% <100.00%> (-0.10%)	⬇️
...ests/tests_integration/test_api/test_datapoints.py	99.36% <100.00%> (+0.01%)	⬆️

... and 6 files with indirect coverage changes

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.