[rust] Formatting and clippy fixes

Summary:
ENG-6452 : Lint staged fails on Rust formatting

After nix update, rustfmt started formatting let else which meant that lint-staged was failing. I took this opportunity to also fix some low-hanging clippy fixes.

Test Plan:
In each cargo project:

• Run cargo fmt
• Run cargo clippy
  • If there are any quick and safe fixes do them
  • If I applied any clippy fixes I also run cargo check && cargo check --tests after that

Reviewers: bartek, varun, kamil

Reviewed By: kamil

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D10651