Improve Item validation rules and add support for py3.12

[thomas-maschler]

• Require type property to be set for Catalog and Collections
• Fix validator for Item datetime and Common MetaData start_datetime and end_datetime
• Make sure all datetime fields are correctly parsed
• Include datetime and license to Common MetaData
• Make sure default values for required but unset fields are correctly parsed
• Add support from Python 3.12
• Lint all files
• Increase test coverage

[vincentsarago]

thank for this great PR @thomas-maschler, I wonder if you've seen #131 where we talked specifically about the datetime validation/parsing

[thomas-maschler]

@vincentsarago, I just noticed that PR. Should have checked first. However, this PR is mostly complementary.

I could either wait until #131 is merged into main or merge those changes into mine to consolidate.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

❗ No coverage uploaded for pull request base (main@c03272e). Click here to learn what that means.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #134   +/-   ##
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  Coverage        ?   96.99%           
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  Files           ?       26           
  Lines           ?      632           
  Branches        ?        0           
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  Hits            ?      613           
  Misses          ?       19           
  Partials        ?        0           

Flag	Coverage Δ
unittests	96.99% <100.00%> (?)

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[thomas-maschler]

Closing this PR in favor of #135. The new PR is branched of #131 and I will keep it in draft until #131 is merged.