Change the `CONTRIBUTING.md` guidelines to order function arguments.

```Makes sense, it should probably be part of the `CONTRIBUTING.md` guidelines. Something like: first owned values, then mutable owned values, then immutable refs, then mutable refs, then closures.```

_Originally posted by @SupremoUGH in https://github.com/Manta-Network/manta-rs/pull/356#discussion_r1231968315_

Change the guidelines and apply them to the codebase.