Add unit testing for `R/process_knb_to_duckdb.R`

[theamarks]

Currently exploreARTIS R package does not have formal unit testing set up. We need testing for the new function that will also setup the testing framework for the entire package.

• structure R package unit testing according to guidelines --> https://r-pkgs.org/testing-design.html
• use many comments in testing scripts as these will provide examples for future package test development
• When submitting Github PR to exploreARTIS/develop-build-knb-duckdb branch please reference issue numbers in commit and PR text body so issue will be automatically pulled through future dev PRs. This automatically closes issues with commits and PRs.

Github issue autolink syntax:

• fix #xxx
• fixes #xxx
• fixed #xxx
• close #xxx
• closes #xxx
• closed #xxx
• resolve #xxx
• resolves #xxx
• resolved #xxx

Other resources:

• https://mtlynch.io/good-developers-bad-tests/