Improvements prompted by clippy, and disable one lint

Improvements prompted by current nightly's clippy.

Also disable one lint which I think is in rather poor taste.

assigned to @Diziet

requested review from @eta

added 13 commits

• 67f8843a...b137be22 - 10 commits from branch tpo/core:main
• 4a06ce01 - clippy: Drop an unused lifetime
• 07175957 - clippy: Use write! rather than push_str, format
• 0cc94d44 - clippy: Change a binding to (), and allow clippy::let_unit_value

Compare with previous version

Rebased to fix conflict with my own other MR...

approved this merge request

I feel like normally I'd get annoyed at disabling a default lint... but I do agree, that is a particularly dumb lint.

merged

mentioned in commit aaf133de