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/5q/zcc7tkt11f13mhczs1yfd4qc0000gn/T/Rtmpe0vmNF/temp_libpath252f4dccb1e2/opusreader2/extdata/test_data/test_spectra.0"