Adds flit to build project

[skrawcz]

We switch to flit on the recommendation of apache airflow.

Note: flit does not handle tuples for versions, so we have to duplicate this information for now. I have submitted a PR that they will hopefully accept to fix this.

Changes

• pyproject.toml

How I tested this

• flit build works

Notes

Checklist

• PR has an informative and human-readable title (this will be pulled into the release notes)
• Changes are limited to a single goal (no scope creep)
• Code passed the pre-commit check & code is left cleaner/nicer than when first encountered.
• Any change in functionality is tested
• New functions are documented (with a description, list of inputs, and expected output)
• Placeholder code is flagged / future TODOs are captured in comments
• Project documentation has been updated if adding/changing functionality.

[skrawcz]

I'm going to ignore that unit test -- test_huggingface_extensions related.