Various fixes and improvements

[blag]

Fix and improve a many small things.

Description

• Switched to try importlib.metadata first (Python 3.8+), then fall back to pkg_resources.get_distribution
• Ignored the new admin.W411 warning
• Use pathlib in tests/settings.py - much more readable
• Minimized test matrix in GHA and Tox configs to only test supported pairs of Python/Django
• Fix a flake8 check regarding warning.warn
• Use f-strings where possible, because they're awesome
• Created infrastructure to generate mmdb files for testing, and use them in tests (more on this below)
• Silence warning during tests about IP address not found in database (silenced it by testing for it)
• Added city and country templatetags, since they might be useful for people
• Use a timezone-aware now() in tests
• Add continue-on-error to GHA steps that test with a -dev Python version or use Django from the main branch

I noticed that some tests weren't running because we didn't have a valid mmdb database from MaxMind. But, we would need a MaxMind account to download their mmdb files. Additionally, even if we did manage to download those files from MaxMind within tests, we would be testing against real world data that could change out from under us - this actually happened in some of the tests with an IP address that the tests expected to be in San Diego. I wrote a Perl script using MaxMind's mmdb writer Perl library to write minimized mmdb fixture files. I had to reverse engineer the Perl data structures so that the generated files would be properly readable by Python's geoip2 library, but the result is two very small binary mmdb files that only contain IP addresses we need for tests.

Motivation and Context

Silences various warnings during tests, improves GHA test time, modernizes Python syntax, ensures all tests are run in a repeatable manner without relying on third party non-static data, and adds some nice-to-haves.

How Has This Been Tested?

Screenshots (if appropriate):

Types of changes

• [x] Bug fix (non-breaking change which fixes an issue)
• [x] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• [x] My code follows the code style of this project.
• [ ] My change requires a change to the documentation.
• [ ] I have updated the documentation accordingly.
• [ ] I have added tests to cover my changes.
• [x] All new and existing tests passed.

[codecov[bot]]

Codecov Report

Merging #166 (840b263) into master (8ebdfe8) will increase coverage by 2.29%. The diff coverage is 90.74%.

@@            Coverage Diff             @@
##           master     #166      +/-   ##
==========================================
+ Coverage   92.62%   94.92%   +2.29%     
==========================================
  Files          16       16              
  Lines         746      768      +22     
  Branches       50       65      +15     
==========================================
+ Hits          691      729      +38     
+ Misses         45       29      -16     
  Partials       10       10              

Files	Coverage Δ
tests/settings.py	100.00% <100.00%> (ø)
tests/tests.py	100.00% <100.00%> (+1.63%)	:arrow_up:
tests/utils.py	97.05% <100.00%> (ø)
user_sessions/admin.py	100.00% <100.00%> (ø)
user_sessions/templatetags/user_sessions.py	90.27% <66.66%> (+18.61%)	:arrow_up:

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[WhyNotHugo]

I think that the remaining changes/commits are fine :+1:

[blag]

@WhyNotHugo Thanks for your review! I reformatted the usage section a bit and it's looking much cleaner.

I like your other suggestions, but I think this PR has already caused enough churn. Instead, I have captured your ideas in issues #167 and #168. Both of those should be fairly straightforward to implement, so perhaps we can get a new contributor to submit PRs for those.

I will wait one week or until you give a final 👍 for this before merging it myself (unless I'm told otherwise).