mismatched_lifetime_syntax lint refactors and optimizations

[camsteffen]

I found several opportunities to return early so I'm hoping those will have a perf improvement. Otherwise, it's various refactors for simplicity.

[rustbot]

r? @fee1-dead

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[rustbot]

This PR was rebased onto a different master commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

[jieyouxu]

@bors try @rust-timer queue

[rust-timer]

Awaiting bors try build completion.

@rustbot label: +S-waiting-on-perf

[rust-bors]

⌛ Trying commit c4074bd with merge 449ebb3…

To cancel the try build, run the command @bors try cancel.