IntanRawIO: Update support of `rhs` files

[zm711]

This will be adding support for RHX rhs files with a separate header for rhs files. We haven't officially update RHS support since RHS 1.0 and we are on 3.x so this may take a bit of work. We will add tests files soon so that we can properly test this.

TODOS

• [x] ~~Add support for supply and aux channels in RHS~~ Turns out that there isn't any from newest docs!
• [x] Add support for one-file-per-signal
• [x] Add support for one-file-per-channel
• [x] Add test files for new formats
• [x] Add access to digital channels like we did for rhd
• [x] Try to understand the stim channels to see if we need to make updates
• [x] Add channel_number_dict for one-file-per-signal
• [x] Add analog-out in the one-file-per-channel-dict function

Neuroconv provenance https://github.com/catalystneuro/neuroconv/issues/789