migrate from testthat to tinytest

[JustinMShea]

Much more stable, eliminates issues related to sprawling dependencies that have cropped up in the past with testthat.

https://github.com/markvanderloo/tinytest

Fix test issues related to these missing data -R CMD check ERROR
── Error (test-repExposures.R:3:1): (code run outside of test_that()) ────────
Error: object 'stocks145scores6' not found
── Error (test-repReturn.R:4:1): (code run outside of test_that()) ───────────
Error: object 'stocks145scores6' not found
── Error (test-tsPlotMP.R:4:1): (code run outside of test_that()) ────────────
Error: object 'stocks145scores6' not found

[JustinMShea]

This is complete, all tests cleaned up and passed