Dict override syntax to allow standard form: --cfg.dict.key val

[ganatraad]

What does this PR do?

Fixes #823

To summarize, if the config class has a dict member, then the override was of the form
--cfg.dict '{"key": val}'
This PR allows passing in --cfg.dict.key val
The existing syntax is still valid.

Before submitting

• Did you read the contributing guideline?
• Did you update the documentation? (readme and public docstrings)
• Did you write unit tests such that there is 100% coverage on related code? (required for bug fixes and new features)
• Did you verify that new and existing tests pass locally?
• Did you make sure that all changes preserve backward compatibility?
• Did you update the CHANGELOG including a pull request link? (not for typos, docs, test updates, or minor internal changes/refactors)

[mauvilsa]

Thank you so much for contributing! The fix in _typehints.py file looks good.

Please:

• Change the pull request title to something that summarizes what is being fixed.
• In the changelog only a single entry with a description similar to the pull request title and a link only to the pull request, not the issue. Also it should be in the already existing Fixed subsection.
• Add a unit test, that should fail without the _typehints.py fix.

[ganatraad]

Addressed the comments cc @mauvilsa

[mauvilsa]

The test is not the same case as #823. Please fix.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (10cfd30) to head (27edf8e).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main      #824   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           24        24           
  Lines         7234      7237    +3     
=========================================
+ Hits          7234      7237    +3     

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