IRMAS instrument tagging is not parsed correctly

[GCPhillips]

Some of the IRMAS training files do not contain a genre tag at the end of the file name, and instead is an instrument tag. For example, if the training track with id 0001__1 is loaded, the genre will be cla and instruments will only contain cel, even though both are instruments and there is no genre tag:

In the code, a check could be performed to see if the parsed out string inside the brackets is in INST_DICT.

[mnlscn]

Hi! I'd like to work on this.

While digging into the parser I hit an ambiguity worth flagging before writing the fix: cla appears in both INST_DICT (clarinet) and GENRE_DICT (classical), so "check if the tag is in INST_DICT" doesn't fully resolve the case.

I see three possible rules:

1. INST_DICT wins: if a tag is in INST_DICT, always treat it as instrument (even if it's also in GENRE_DICT). Fixes the reported [cel][cla] case, but genre becomes None for every classical file —> breaking the existing behaviour.
2. GENRE_DICT wins: treat a tag as genre if it's in GENRE_DICT, regardless of INST_DICT. Preserves classical genre annotations, but does not fix the reported case.
3. INST_DICT wins + surface second instrument: same as (1), but also append the second bracketed tag to the instrument list when it's an instrument code. Closest to the instrument==['cel','cla'] goal in the issue, but the most invasive change.

Which rule should the fix follow? Happy to open a PR as soon as there's a decision on this.