Fix clippy warnings

Right now some clippy warnings are allowed in the code. They look something like this:

https://github.com/dandavison/delta/blob/15d06cbf7584570ec3b5beaba99cb8898f9ec3dc/src/paint.rs#L243

So just search for the word "clippy" in the code and you will find them.
You should do the following:

1. run cargo clippy and check that there are no warnings
2. delete the allow line
3. run cargo clippy and check that you have a warning now
4. try to fix the warning

The only one you should not remove MAYBE it's `#[allow(clippy::tabs_in_doc_comments)]`. But I am not sure about this.

Search the codebase for "clippy" and inspect the allow line linked in src/paint.rs. Run cargo clippy, remove each applicable allow, rerun it to confirm the warning, and fix the warning; verify cargo clippy finishes without warnings, while assessing whether tabs_in_doc_comments should remain.

Written by the indexing model from the issue text.