refacto(air/layout): move compute_program_hash in utils.rs

[tdelabro]

Tell me if it's fine for it to leave in utils.rs

[Okm165]

I think that better idea is to not create another file lets move this function to mod.rs there are some common utils there already so it fits in imo
https://github.com/tdelabro/swiftness/blob/factorize-compute-program-hash/crates/air/src/layout/mod.rs#L114

[tdelabro]

@Okm165 done

Sidenote: more than half of this file is Error definition. Maybe moving those into their own error.rs could make sense

[Okm165]

LGTM
write comment here when u finalized everything i will merge

[tdelabro]

@Okm165 I moved the errors to their own file.

Btw, is there a reason why you prefer to duplicate the error structs and use both thiserror and thiserror-nostd, rather than using only the latter but with or without its std feature: https://docs.rs/crate/thiserror-no-std/latest/source/Cargo.toml.orig

[Okm165]

@tdelabro No particular reason
I wasn’t aware of this feature in thiserror-nostd. Feel free to improve it if you'd like!

[tdelabro]

@Okm165 I will on a separated PR as it spans changes across multiple crates