Add timezone consistency across deployments & UI

[ml-evs]

This PR enforces UTC for all datetimes stored by datalab, via:

• updating the underlying model so that any missing timezone from a user/script is interpreted as UTC. This is done at the validator level, so some inconsistencies might arise in old data that has not previously been stored with a timezone, but the API at least will always validate and fix it this now. I explicitly added the timezones into remote fs checking so that we don't have to worry about mongo version compatibility.
• The app code can now assume that a missing timezone really does mean UTC, and all future timestamps should have the 00:00 UTC offset suffix.
• App code now has to have a custom computed setter/getter for datetime objects, so that we can cast the format from HTML <input format='datetime-local'> into the full isoformat stamp.
• all internal datetimes now use UTC explicitly, with enabling of the ruff DTZ/flake8-datetimez linting rules

Closes #440

Assorted fixes:

• the IsoformatDateTime wrapper was also setting a bad JSON Schema type, for some reason -- this is removed
• The File model wasn't using the extended datetime format for time_added.

Relatedly (from HN today...): https://ssoready.com/blog/engineering/truths-programmers-timezones/

[cypress]

datalab    Run #2712

Run Properties:   Passed #2712  •  0cfa8498f3 ℹ️: Merge 606408e076347421c96b8f2ff746892d45c08469 into 509f04f3d194eb7838060905df07...

Project	datalab
Branch Review	ml-evs/datetime-fixes
Run status	Passed #2712
Run duration	06m 11s
Commit	0cfa8498f3 ℹ️: Merge 606408e076347421c96b8f2ff746892d45c08469 into 509f04f3d194eb7838060905df07...
Committer	Matthew Evans
View all properties for this run ↗︎

---

Test results
Failures	0
Flaky	0
Pending	0
Skipped	0
Passing	405
View all changes introduced in this branch ↗︎

[codecov]

Codecov Report

Attention: Patch coverage is 74.07407% with 7 lines in your changes missing coverage. Please review.

Project coverage is 68.43%. Comparing base (509f04f) to head (618290c).

Files with missing lines	Patch %	Lines
pydatalab/src/pydatalab/file_utils.py	28.57%	5 Missing ⚠️
pydatalab/src/pydatalab/remote_filesystems.py	87.50%	1 Missing ⚠️
pydatalab/src/pydatalab/routes/v0_1/collections.py	50.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #970      +/-   ##
==========================================
+ Coverage   68.42%   68.43%   +0.01%     
==========================================
  Files          62       62              
  Lines        3933     3935       +2     
==========================================
+ Hits         2691     2693       +2     
  Misses       1242     1242              

Files with missing lines	Coverage Δ
pydatalab/src/pydatalab/backups.py	48.59% <100.00%> (ø)
pydatalab/src/pydatalab/models/files.py	100.00% <100.00%> (ø)
pydatalab/src/pydatalab/models/utils.py	87.57% <100.00%> (-0.08%)	⬇️
pydatalab/src/pydatalab/routes/v0_1/auth.py	63.54% <100.00%> (ø)
pydatalab/src/pydatalab/routes/v0_1/items.py	82.65% <100.00%> (ø)
pydatalab/src/pydatalab/remote_filesystems.py	79.74% <87.50%> (+0.52%)	⬆️
pydatalab/src/pydatalab/routes/v0_1/collections.py	70.45% <50.00%> (ø)
pydatalab/src/pydatalab/file_utils.py	38.83% <28.57%> (ø)

[ml-evs]

This should fix the issue you were seeing @BenjaminCharmes, was just some overzealous refactoring