Utility function that retrieves the location of the sample OPUS binary file on disk.
opus_file()
a character vector storing the location of the sample OPUS file
fn <- opus_file()
fn
#> [1] "/private/var/folders/2s/h6hvv9ps03xgz_krkkstvq_r0000gn/T/RtmpO5YSeW/temp_libpath20da723d0a72/opusreader2/extdata/test_data/test_spectra.0"