fix: Ensure metadata serialization handles numpy.integer properly

[japols]

This PR fixes a bug where int64 objects in the metadata raised TypeError: Object of type int64 is not JSON serializable by converting them to a python-native int.

[FussyDuck]

All committers have signed the CLA.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 72.96%. Comparing base (97c0a99) to head (0cb8f1c).

Additional details and impacted files

@@           Coverage Diff            @@
##           develop     #140   +/-   ##
========================================
  Coverage    72.96%   72.96%           
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  Files           10       10           
  Lines          825      825           
========================================
  Hits           602      602           
  Misses         223      223           

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