fix: change serializer to show enum for upload.state_name

[thomasrockhu-codecov]

Updates the serializer to show as a ChoiceField in the API docs

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Note

Low Risk
Low risk change limited to serializer field typing for API documentation; it should not affect persistence or processing logic, but could slightly change the OpenAPI schema/validation for state_name.

Overview
Updates the v2 commit uploads serializer so state_name is exposed as a ChoiceField backed by UploadState values (instead of a plain string), improving generated API docs and making the allowed states explicit.

Adds the UploadState import and keeps state_name read-only, still sourced from get_state_id_display.

^{Written by Cursor Bugbot for commit 1533dc9. This will update automatically on new commits. Configure here.}

[sentry]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.25%. Comparing base (13ff78c) to head (1533dc9).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #784   +/-   ##
=======================================
  Coverage   92.25%   92.25%           
=======================================
  Files        1305     1305           
  Lines       47981    47982    +1     
  Branches     1636     1636           
=======================================
+ Hits        44263    44264    +1     
  Misses       3407     3407           
  Partials      311      311           

Flag	Coverage Δ
apiunit	96.35% <100.00%> (+<0.01%)	⬆️

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Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ All tests successful. No failed tests found.

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