Enable various new clippy lints

[tgross35]

This applies a most of what is discussed in #349.

Additionally, I enabled a large subset of lints from pedantic that shouldn't be too annoying, but should improve consistency and correctness.

This patchset can be reviewed per-commit, each patch should build correctly. A few things I need feedback on:

1. Which lints should be enabled? I enabled quite a few that I think should be reasonable, but will adjust as needed
2. There are some // SAFETY: TODO comments in rust/kernel/init. I'm not too familiar with how this portion - could somebody more familiar to fill in those blanks and generally verify the safety comments in init
3. Should the patchset be merged or split up more? I'll probably send the first commit separate since that's the only one that touches non-Rust things, but intend to send the others together