Fix findings from Dmitry's review

[jtraglia]

This PR is a work in progress. It does the following things:

• Update com.diffplug.spotless to work with Java 22.
• Rename compute_fk20_proofs to compute_fk20_cell_proofs.
• Hardcode compute_fk20_cell_proofs to accept FIELD_ELEMENTS_PER_BLOB length poly.
• Add instructions to install build in Python bindings.
• Add comment about fr_is_null edge case in recovery.
• Handle zero-length inputs to FFT functions.
• Optimize calculation for coset_factor_pow.
• Replace signed integers with unsigned types.
• Assert that the domain strings are the correct length.
• Add precomputed array of RBL cell indices.

Big thanks to @khovratovich 🙏

If we choose to, we can do larger renaming fixes in a separate PR.

[asn-d6]

Thanks for this. Highlighting some things that can be improved IMO.

[b-wagn]

Thank you @jtraglia and also @khovratovich !

I left some comments, but most of it looks good :)

[b-wagn]

Changes look good to me 👍

[asn-d6]

LGTM! Thanks a lot everyone here!