Lint codebase with clippy

[exdx]

#342 does some QoL linting but there are still some unresolved clippy warnings.

Ideal set of steps:

• Refactor or #[allow(...)] the code to have each warning accounted for
• Update CI to error in case of clippy warnings (see https://github.com/ava-labs/firewood/blob/2db03af7861f88066dd226eebf698fa001f310d3/.github/workflows/ci.yaml#L25 for an example).

After that we will have a fully linted codebase that is more production ready.