Copy `.mif` files into `modelsim/` dir during creation

> testbench-runner could also perform this in `generate_tcl.py`, since this is where the modelsim project dir is created. Just add a line that glob searches for `.mif` files and copies what it finds. That should work for now.

_Originally posted by @benjamin051000 in https://github.com/ARC-Lab-UF/digital-design-grading-tbs/issues/8#issuecomment-1506398259_
            