Relaxed clippy fixes/nits (#2661)

This PR contains just a few clippy fixes and nits, which are, however,
relaxed by workspace clippy settings here:
https://github.com/paritytech/polkadot-sdk/blob/master/Cargo.toml#L483-L506



---------

Co-authored-by: Dmitry Sinyavin <[email protected]>
Co-authored-by: ordian <[email protected]>
Co-authored-by: command-bot <>
Co-authored-by: Bastian Köcher <[email protected]>