[DOP-12026] Typing improvements

[dolfinus]

Change Summary

• Some linters (like Pylance in VS Code) complaining about imports from modules:
  

This is because module lack __all__ attribute, so linter thinks that all these classes are private, and should be imported from nested module. Added __all__ to fix that.

• Added @deprecated decorator for old classes. This allows IDE to highlight classes like this
  

Also updated old classes documentation to include deprecation notice

Related issue number

Checklist

• Commit message and PR title is comprehensive
• Keep the change as small as possible
• Unit and integration tests for the changes exist
• Tests pass on CI and coverage does not decrease
• Documentation reflects the changes where applicable
• docs/changelog/next_release/<pull request or issue id>.<change type>.rst file added describing change
  (see CONTRIBUTING.rst for details.)
• My PR is ready to review.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (602d04f) 96.28% compared to head (f22ebb0) 96.37%.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop      #69      +/-   ##
===========================================
+ Coverage    96.28%   96.37%   +0.08%     
===========================================
  Files           48       48              
  Lines         1049     1075      +26     
  Branches       183      192       +9     
===========================================
+ Hits          1010     1036      +26     
  Misses          23       23              
  Partials        16       16              

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