chore: re-enable clippy lints and fix new lint errors (#6185)
### Description
#6150 [accidentally made clippy warnings
non-blocking](https://github.com/vercel/turbo/pull/6150/files#diff-d34053cb32303b7498893f06e5d45b86ede726954dcb06968b3c6618395dc109L1).
This adds back `#![deny(clippy::all)]` and fixes the Clippy warnings
that were already present.
### Testing Instructions
CI
Closes TURBO-1474
Co-authored-by: Chris Olszewski <Chris Olszewski>
