This is just a suggestion! When looking into the parser, I was sometimes confused by some variable names. Maybe this reduces cognitive load?

1. Some renamings:
   next_pos tocurrent_pos (it's actually current_pos)
   peek() tocurrent() (peek and look_ahead seemed to do the same)

2. Removedeat, since it was only used once

3. Added ais_relevant method which is more readable than!is_irrelevant (to me at least)

and 4. Changed some manualloops to Rust native iterators

Again, just a suggestion – the code was already great, and I don't want to be too invasive 🙌