`Set` storage questions

[ImprovingRigmarole]

Following the few commits I did for #22, I noticed a few things related to the Set struct :

• as IntervalSet is stored on an u32, in modes : the intervals which are popped right will come back from the 31th bit, which won't make those come back into the 0..12 semitones range (in the case of a scale defined on an octave), but there might be other uses where the octave limitation doesn't apply

  also I think maybe it would make more sense if this modes function was part of the ScaleIntervals instead of the generic IntervalSet ?
  (same rotate problem would occur on ScaleIntervals's u16 storage)

• I was wondering why MidiSet hasn't been defined as a Set<MidiNote, u128>, which could avoid the low/high split, and maybe simplify the implementation for future things (like the awful totally unreadable split I did there!)
  maybe it was to avoid u128 being not cffi compatible ? apparently it is since 1.78,
  but since Dioxus is part of the crate, I not so sure about wasm ffi which is likely to get involved then...

• closely related to the previous one, was also wondering why MidiSet doesn't have the Copy derive, since it's only 2 u64 ?

Would be ready to implement those changes myself if needed, just didn't want to change those with a PR coming out of nowhere without asking first !

thanks for this crate btw
I've tried a few other music theory crates before finding this one, but they didn't seem as much versatile