fast paths 🎉

[lcnr]

the new solver can hang when encountering unexpected patterns, especially around aliases. To deal with this we add fast paths to avoid some of the more easily triggerable exponential behavior. We should still list them - and their shortcomings - here.

• -Znext-solver: eagerly normalize when adding goals rust#125343
  • enables the solver to more eagerly detect cycles
  • slightly weakens type inference
  • used to fix endless loop by running cargo test with toolchain 2024-05-14 rust#125269, see added test