Projection extension: migrate Assets on Items

[bmcandr]

Related Issue(s):

• Projection extension's migrate method doesn't migrate Item's Assets #1548

Description:

• Update the Projection extension's migrate method to migrate projection fields on Assets on Items and Item-Assets on Collections.
• Rename test_migrate to test_migrate_item and add test_migrate_collection_item_assets

PR Checklist:

• Pre-commit hooks pass (run pre-commit run --all-files)
• Tests pass (run pytest)
• Documentation has been updated to reflect changes, if applicable
• This PR maintains or improves overall codebase code coverage.
• Changes are added to the CHANGELOG. See the docs for information about adding to the changelog.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 92.41%. Comparing base (e713adf) to head (2f308dc).
Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1549      +/-   ##
==========================================
+ Coverage   91.62%   92.41%   +0.79%     
==========================================
  Files          54       55       +1     
  Lines        7578     8364     +786     
  Branches      923      963      +40     
==========================================
+ Hits         6943     7730     +787     
+ Misses        451      449       -2     
- Partials      184      185       +1     

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[gadomski]

Tight! Thanks for the bugfix!