Apply cargo fmt and clippy suggestions

It looks like my local versions of rustfmt and clippy are perhaps newer than the ones we use for CI, and so they recommend changes that our CI run does not. (Although rustfmt in the CI run complans with “Warning: can't set imports_granularity = Module, unstable features are only available in nightly channel.”)

Perhaps we should also update these tools in our CI containers, but I don’t know whether that’s even possible (other than just waiting for newer versions to be available there).