Compiles the false-positive occupancy model the first time it is needed and
keeps the executable in the user cache directory
(tools::R_user_dir("crywolf", "cache")), so later sessions load it
without recompiling. fp_occu() calls this function itself; call it
directly to compile ahead of time, for example before launching parallel
workers in fp_calibrate().
Details
The model is compiled with threading enabled (stan_threads), so that
fp_occu() can split the likelihood of each chain among several threads
(argument threads_per_chain).