chore: fix clippy warnings (#15944)

Stop allowing clippy::derive-partial-eq-without-eq and fix warnings
about deriving PartialEq without also deriving Eq.

In one case I removed the PartialEq because it a) wasn't necessary,
and b) sketchy because it was comparing floating point numbers.

IMO, that's a good argument for enforcing the lint rule, because it
would most likely have been caught during review if it had been enabled.