old: `actions-rs/toolchain`
new: `dtolnay/rust-toolchain`
fix
ci(fuzz): change runner to ubuntu-latest
ci: update run syntax in fuzz job
ci: update and run fuzz/generate-files.sh
We should probably restore this in the future, but we need to rethink
how we fuzz hashes -- right now when cfg(fuzzing) is set, we break all
the hash functions in a way that won't match any other library.
We should probably make this breakage opt-in but this will require
buy-in from rust-lightning and maybe others.