Cutover to duckdb for unit tests

[dogversioning]

This PR does the following:

• Removes athena based cursor mocking in favor of duckDB for CLI testing
  • athena is still covered by our regression environment
• Adds a simple test for the core study (and validation data)
• Some light tweaks to some of the mock studies to make more sense being run in a real db
• Clears env for the duckdb test to prevent overriding behavior

Checklist

• Consider if documentation (like in docs/) needs to be updated
• Consider if tests should be added
• Run pylint if you're making changes beyond adding studies
• Update template repo if there are changes to study configuration