table comparison testing via dataframes

@cdolfi has potentially identified a new way to use dataframe comparisons to ensure data hasnt changed.

This may be a useful tool for validating the outputs of a materialized view for a known repo. Especially to ensure that any internal changes to core tables are also made in the mat view queries and thus do not impact the actual output data in the views that will become the downstream database API interface.

Implementing this testing will be a useful prereq for #324