reorganize tests, make devdeps testing optional, unpin latest Python testing, and prepare for possibility of data caching

[zacharyburnett]

Resolves SCSB-79

This PR reorganizes CI tests and moves devdeps tests to a new optional workflow that can be started with the label run devdeps tests

Checklist

• [x] ~added entry in CHANGES.rst (either in Bug Fixes or Changes to API)~
• [x] updated relevant tests
• [x] ~updated relevant documentation~
• [ ] updated relevant milestone(s)
• [x] added relevant label(s)

[codecov[bot]]

Codecov Report

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