Loosen dependancies for `click` and `requests`, removes `six` dependancy

[pndurette]

This PR,

• Removes the dependancy on six (only needed for Python 2.7 compatibility)
• Loosens the dependancy on click and requests
• Re-organizes imports

Also,

• Adds pyproject.toml to the triggers for the unit tests GitHub Action

Fixes #388

[codecov[bot]]

Codecov Report

:exclamation: No coverage uploaded for pull request base (main@3667f06). Click here to learn what that means. The diff coverage is n/a.

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