Fix clippy warnings and run rustfmt

[mkrasnitski]

Clippy was complaning about some uses of std::mem::transmute, so I changed them to use simple as casting instead. Additionally, ran cargo fmt --all to avoid extraneous formatting changes from leaking into future PRs.

[emesare]

Due to the nature of formatting all of the rust api, we are instead going to format the code in rust_break_everything. Those refactors also will create large diffs, and doing them both at the same time is better than if we were to go ahead and format now, then follow it shortly after with another large refactor.

I am going to keep this PR up until rust_break_everything is merged.