packaging/maintenance: compile `papiex` for `epmt` via `pip`

[ilaflott]

compile_papiex.sh is not going to be fun to maintain, CMake with (or maybe even without) scikit-build-core could be more helpful.

Originally posted by @ilaflott in #171 (comment)

this was suggested to me by @fmalatino after his experience with the custom-pip install hook and exploring alternatives in NOAA-GFDL/pyFMS#39 .