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/0g/hj_q_pzx65bbjnslxz9n0src0000gn/T/RtmpyIjlcn/temp_libpath194b2c0ee6d9/opusreader2/extdata/test_data/test_spectra.0"