[gguf & st] parse shard filenames in typed function

[mishig25]

follow up to #627 (review)

why not a typed function fn(filename) that returns all the data in a typed manner instead of the regex 🙈 .
Currently in the next version of HF.js we can change the regex to something else, removing or renaming the groups, and on moon's side we'd have no clue. No compiler warning or anything.

[coyotte508]

thanks

[julien-c]

in most cases it's useful to wait a little more than 10 mins before merging 🥲

(LGTM)