fix clippy lints and other minor improvements

[abysssol]

I was planning on creating a pull request to improve ofborg's behavior when requesting reviews, but noticed that clippy was emitting a lot of warnings and an error. So, I decided to start by fixing them, and along the way ended up adding other assorted improvements as well.

The project appears rather outdated and unidiomatic in general. It seems a partial rewrite may be in order. Most of the dependencies should probably be updated or replaced (traitobject isn't sound since it assumes the layout of fat pointers, but won't be fixed since it's unmaintained). Would there be any problems with replacing hubcaps with octocrab?

Notable commits: 07c2ccf1123c842267d67cb3f6fb16030663e33b 9925e497a77f9c55d67a4750e3d715d6ac0c1b7e 5299de378ef8e4546ae1a2954ec3e32210f9678c