Fix clippy lints

[jayvdb]

fwiw, I am working on a feature, so would like the abundance of preexisting clippy lints to be cleared so I can keep my own code tidy.

I have not fixed three clippy lints that need a little more investigation or discussion. I dont mind a few clippy lints appearing, as I can still easily see any lint problems that are being introduced by me.

[kamadak]

Thank you for the patch.
I will merge some parts (e.g., std::u64::MAX --> u64::MAX, which was not used before to support Rust 1.40 and I have now dropped support for that version), but may not merge some parts that I do not like (e.g, .map(|&x| x) --> .copied(), which breaks symmetry with the surrounding code and increase my cognitive load.

Anyway, reducing clippy lints is generally good, so I will try, thanks.

[jayvdb]

I have removed the .copied() replacements that break symmetry, and added a lints.clippy table in Cargo.toml to tell clippy which lints you dont want warnings about.

Feel free to simple put "revert" on other bits of the PR that you dont like, and I will revert them and tell clippy to stop warning about those in future.