Update clippy version in CI and fix new lints

[newpavlov]

Closes #1187

[tarcieri]

The der related problems are actually a regression/missing feature in clippy, now that arithmetic_side_effects has subsumed the integer_arithmetic lint: rust-lang/rust-clippy#11220

It assumes any math with core::ops traits is unsafe, even on user-defined types which prevent those problems (in the case of der, with fallible results to arithmetic operations).

There's a suggestion to add a feature to clippy to hint to it that a given type's arithmetic is safe, but right now there's no solution other than disabling the lint.

[newpavlov]

@tarcieri
It does not look like the Clippy issue will be resolved in the near future. Can I merge this PR or would you like to make some changes?

[tarcieri]

Ideally I'd like to see arithmetic_side_effects fixed so it provides the same functionality integer_arithmetic had before it was replaced. Otherwise merging will be a regression.

But if you want to merge it, I guess that's fine. It's just an annoying regression.

[newpavlov]

Maybe it's worth to ask Clippy developers to return integer_arithmetic as a subset of arithmetic_side_effects? I would prefer to merge this PR now, since warnings in IDE are quite annoying for me and I would prefer to fix the lints to tweaking toolchain version or disabling Clippy.

[tarcieri]

It just needs a new annotation for arithmetic-safe newtypes as described in rust-lang/rust-clippy#11220 (comment)