Add tests for DictPropertyBag and type hints for IPropertyBag.

[junkmd]

This PR adds a new test class, Test_DictPropertyBag, to test the IPropertyBag interface's functionality via the DictPropertyBag implementation.
This includes tests for:

• Reading existing properties.
• Writing new properties.
• Updating existing properties.
• Handling attempts to read non-existent properties.

Additionally, this introduces type hints for the IPropertyBag interface methods (Read and Write) within a TYPE_CHECKING block.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 83.52%. Comparing base (8dcee01) to head (8fb2a75).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #860      +/-   ##
==========================================
+ Coverage   83.35%   83.52%   +0.16%     
==========================================
  Files         123      123              
  Lines       11300    11325      +25     
==========================================
+ Hits         9419     9459      +40     
+ Misses       1881     1866      -15     

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