Add integration tests using hubData

[annakrystalli]

Background

As a complete test of data integrity during transformation to parquet, it would be good to test that transformed hub data accessed through hubData is consistent with data prior to transformation.

Required work

We'll need R testing framework scaffolding. Not sure what exactly that would entail (how minimal it can be) as I've only ever included test suites as part of packages.

Requirements to be considered done

• An R testing framework (including a CI workflow)
• Tests that check NA values and mixed output_type_id data type columns (including different data types across separate files which should ensure data successful schema application by connect_hub()) are consistently recovered/encoded post transformation

[annakrystalli]

See discussions in #1 for extra context