Use timezone.now() for Django CMS timestamps while keeping local times for SourceImage

[coderabbitai]

Context

In PR #987, a code review suggested using timezone.now() instead of datetime.now() for the Job model's finished_at field. This change was deferred due to the nuanced timezone requirements in the codebase.

Description

The codebase currently has mixed timezone handling:

• Uses datetime.now() for Job timestamps and other Django CMS operations
• Project is configured with USE_TZ=False

However, there's a nuanced requirement that needs to be addressed:

SourceImage timestamps (keep as local time)

• SourceImage timestamps should remain local time only
• These represent the actual local time when images were captured
• Converting to UTC would introduce errors for these timestamps
• No changes needed for SourceImage

Django CMS operations (should use timezone-aware)

• Job.finished_at and similar Django CMS timestamps should be timezone-aware
• Web users need to see when jobs started/finished in their local time
• Currently these are naive datetimes, making it difficult to display correctly across timezones

Proposed Change

1. Keep SourceImage timestamps as local time (no changes)
2. Migrate Job.finished_at, Job.started_at, and similar Django CMS fields to use timezone.now()
3. Consider enabling USE_TZ=True for the Django project, while ensuring SourceImage timestamps remain local
4. Update any related timestamp handling to maintain the distinction between local-only and timezone-aware timestamps

References

• PR: Distributed Worker Architecture for ML Processing (Processing Service V2) pt. 1 #987
• Comment: https://github.com/RolnickLab/antenna/pull/987#discussion_r[comment_id]
• Requested by: @mihow