For PFA/Tetris, this sources all .R files under inst/extdata/<backend>/.
For PFA, it also compiles PFA.cpp (if present) via Rcpp::sourceCpp().
For PFA/Tetris, this sources all .R files under inst/extdata/<backend>/.
For PFA, it also compiles PFA.cpp (if present) via Rcpp::sourceCpp().