fix: clippy lints

[sonicfromnewyoke]

Problem

ci command cargo clippy --all-targets reports a lot of warnings

this is an initial step to more strict linting of the project, related to #352

Summary of Changes

• apply suggestions where this is pretty safe
• add #[allow(clippy::await_holding_lock)], #[allow(clippy::too_many_arguments)], and #[allow(clippy::large_enum_variant)] to places that require extensive refactoring

[lgalabru]

Thanks @sonicfromnewyoke!
iirc @Aursen added a step cargo +nightly fmt --all to the CI, should we also add cargo clippy --all-targets? Stable? Nightly?

[Aursen]

I used nightly for the imports

[sonicfromnewyoke]

Thanks @sonicfromnewyoke! iirc @Aursen added a step cargo +nightly fmt --all to the CI, should we also add cargo clippy --all-targets? Stable? Nightly?

i believe --all-targets is useful, because I have already added a couple of dependency issues to that project, that were fixed by you afterward, due to shallow checks