Bump python, `dlclibrary`, switch to pip install in tests

[sneakers-the-rat]

Sorta orthogonal duplicate related to https://github.com/DeepLabCut/DeepLabCut-live/pull/110 , thought it was worth a separate PR because it's sorta different from deciding on the tf cap, but involves it. so this probably needs modification/rebasing on whatever gets decided there but just wanted to have a (hopeful) fix for the tests on the books. this should also be a patch version bump and re-release whenever it and 110 get merged, not done in this PR.

tests failing because can't find url for model. updates in dlclibrary reflect those changes, but tests install old version because lockfile hasn't been updated.

so:

• update deps:
  • python 3.7 is EOL
  • match last supported TF of DLC at 2.10
  • bump dlclibrary to current known good version
• relock
• run tests from pip install instead of poetry: poetry install good for tests when actively developing for reproducible environments with resolved dependency trees. since we're not actively developing this though, tests can get stale and fail to reflect the environment created when people install from pip, which use the pyproject.toml constraints rather than the lockfile. also since sunset is in near future, let's switch to pip install for maintenance reasons.

[sneakers-the-rat]

also seems like python-package.yaml action should be removed, but didn't want to do too much in one pr yno

[MMathisLab]

Cc @jeylau