Fix typing of DatapointSubscription.time_series_count

[erlendvollset]

• Make DatapointsSubscription.time_series_count nullable as per service contract
• Bump version and update changelog

Description

Please describe the change you have made.

Checklist:

• Tests added/updated.
• Documentation updated. Documentation is generated from docstrings - these must be updated according to your change.
  If a new method has been added it should be referenced in cognite.rst in order to generate docs based on its docstring.
• Changelog updated in CHANGELOG.md.
• Version bumped. If triggering a new release is desired, bump the version number in _version.py and pyproject.toml per semantic versioning.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.53%. Comparing base (9ae8db0) to head (1622dd8).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2147      +/-   ##
==========================================
- Coverage   90.53%   90.53%   -0.01%     
==========================================
  Files         158      158              
  Lines       23753    23753              
==========================================
- Hits        21505    21504       -1     
- Misses       2248     2249       +1     

Files with missing lines	Coverage Δ
cognite/client/_version.py	100.00% <100.00%> (ø)
...te/client/data_classes/datapoints_subscriptions.py	87.61% <ø> (ø)

... and 1 file 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.

[psalaberria002]

🦄