ui tests take a very long time

[lcnr]

• tests/ui/issues/issue-29466.rs
  • fixed by Do not gather local all together at the beginning of typeck rust#140561
• tests/ui/numbers-arithmetic/saturating-float-casts.rs
• tests/ui/suggestions/fn-to-method-deeply-nested.rs
• tests/ui/async-await/async-closures/post-mono-higher-ranked-hang.rs

these three tests take more han 60 seconds but do eventually compile. There's likely some trivial perf fix for them we should impl in the new solver.