Safely handle datetime constraint values with and without timezone info

[jacob-indigo]

Description

The Unleash web app provided timezone info when creating date constraints so this PR updates the client to also provide timezone info for datetime objects it creates. And then gracefully fall back to UTC if an ISO string is received with no timezone info.

Fixes #323

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

How Has This Been Tested?

Please describe the tests that you ran to verify your changes.

• Unit tests
• Spec Tests
• Integration tests / Manual Tests

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

[coveralls]

coverage: 96.545% (-0.5%) from 97.05%
when pulling 19a3e31 on jacob-indigo:fix_tz_aware_naive_comparison
into 54f00b5 on Unleash:main.

[sighphyre]

Okay I thought about it, this might not be perfect for maintenance reasons but I believe the flow is more or less correct and since this code is going away in the next major, I see no harm in merge + releasing this as a patch