Bring clippy into ci for cleaner code

[xizheyin]

I was modifying the code and realized that there are a lot of places where style could be improved, I scanned it with clippy and found a very large number of warnings. is there a need to bring clippy into CI?

[apiraino]

Someone already sent a while ago a patch to fix clippy lints #1758

IMHO (I am not a maintainer of this repo) I think the first wave of fixes should be manual and carefully reviewed because things may break. Also we probably don't want to apply blindly any clippy lint.

[xizheyin]

Make sense, and it would be better if each lint was divided into different commits. I do think there is a need to do some of that. For example, I had some unused code in my PR submission that would not be detected, and I discovered this manually. I don't know if it's a problem with rust-analyzer.