ENG-3828: Fix Pydantic serializer warning for AnyHttpUrlStringRemovesSlash

[mikeGarifullin]

Ticket https://ethyca.atlassian.net/browse/ENG-3828

Description Of Changes

AnyHttpUrlStringRemovesSlash was declared as Annotated[AnyHttpUrl, AfterValidator(...)], but the AfterValidator returns a plain str. At serialization time Pydantic still expected an AnyHttpUrl instance and emitted a PydanticSerializationUnexpectedValue warning whenever the field held a real value.

Concretely surfaced in the celery task Saving record(s) of current preferences and historical preferences for consent reporting after ENG-2488 switched url_recorded from SafeStr to AnyHttpUrlStringRemovesSlash:

UserWarning: Pydantic serializer warnings:
  PydanticSerializationUnexpectedValue(Expected `<class 'pydantic.networks.AnyHttpUrl'>` but got `<class 'str'>` with value `'https://suscripciones.condenastamericas.com'` - serialized value may not be as expected.)

Attach a PlainSerializer(return_type=str) so the serializer type matches what the validator actually produces. No behavioral change to the output value (still str with trailing slash stripped), but the warning is gone and the field now round-trips cleanly.

Code Changes

• src/fides/api/custom_types.py — added PlainSerializer to AnyHttpUrlStringRemovesSlash.
• tests/lib/test_custom_types.py — new TestAnyHttpUrlStringRemovesSlash covering validation, trailing-slash stripping, invalid-URL rejection, None passthrough, and a regression test that promotes the serializer warning to an error.

Steps to Confirm

1. Run nox -s "pytest(lib)" (or docker exec fides /opt/fides/bin/python -m pytest tests/lib/test_custom_types.py) — all 208 tests pass, including the 11 new ones.
2. Verify regression coverage: revert only the custom_types.py change and re-run TestAnyHttpUrlStringRemovesSlash::test_serialization_does_not_warn — it fails with the exact PydanticSerializationUnexpectedValue warning quoted above.
3. In a Fidesplus environment, trigger the consent-reporting celery task with a non-null url_recorded — the warning no longer appears in worker logs.

Pre-Merge Checklist

• All CI pipelines succeeded
• CHANGELOG.md updated (follow-up commit on this PR)
• No migrations
• No documentation updates required

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2 Skipped Deployments

Project	Deployment	Actions	Updated (UTC)
fides-plus-nightly	Ignored	Preview	May 14, 2026 9:12pm
fides-privacy-center	Ignored		May 14, 2026 9:12pm

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 85.59%. Comparing base (b3374c0) to head (c451054).
⚠️ Report is 5 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #8193   +/-   ##
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  Coverage   85.59%   85.59%           
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  Files         658      658           
  Lines       42847    42847           
  Branches     5018     5018           
=======================================
+ Hits        36675    36676    +1     
  Misses       5064     5064           
+ Partials     1108     1107    -1     

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