feat: Simplify revocation reason handling and update timestamp to be timezone aware (AAI-560)

[minh-biocommons]

Description

AAI-560: Simplify revocation/rejection reason handling and update timestamp to be timezone aware

Changes

• Simplified revocation/rejection reason as the front-end can already use updated_by and updated_at from the response
• Update the updated_at timestamp to be timezone aware so that the front-end can format it correctly

Checklist

• I have commented my code, particularly in hard-to-understand areas
• I have added unit / integration tests that prove my fix is effective or that my feature works
• I have run all tests locally and they pass
• I have updated the documentation (if applicable)
• For any new secrets, I have updated the shared spreadsheet and the GitHub Secrets.

[Copilot]

Pull request overview

This PR simplifies revocation/rejection reason handling by removing automatic concatenation of timestamp and actor information, making the frontend responsible for displaying this metadata using the updated_by and updated_at fields already included in API responses. Additionally, it makes all datetime columns timezone-aware at the database level for PostgreSQL.

• Removed the _reason_with_metadata helper function that was appending timestamp and actor email to reasons
• Updated database schema to use timezone-aware timestamps (TIMESTAMP WITH TIME ZONE for PostgreSQL)
• Added defensive timezone handling in get_data() methods for backward compatibility

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
db/models.py	Removed _reason_with_metadata function; updated DateTime fields to use timezone=True; simplified revoke() and reject() methods to store raw reasons; added defensive timezone handling in get_data() methods
db/types.py	Changed datetime type to AwareDatetime for updated_at fields in data models; removed unused datetime import
migrations/versions/c5ec222dd539_make_datetime_columns_timezone_aware.py	Added Alembic migration to convert existing timestamp columns to timezone-aware for PostgreSQL while preserving SQLite compatibility
tests/test_admin.py	Updated test assertions to expect simplified reasons without timestamp/actor metadata; removed unused freeze_time import and frozen_time fixture
tests/db/test_models.py	Updated test assertions to expect simplified reasons; removed freeze_time usage from revoke tests while preserving it for other tests that still need it

[amandazhuyilan]

Super!