Auto merge of #131911 - lcnr:probe-no-more-leak-2, r=compiler-errors

refactor fudge_inference, handle effect vars

this makes it easier to use fudging outside of `fudge_inference_if_ok`, which is likely necessary to handle inference variable leaks on rollback.

We now also uses exhaustive matches where possible and improve the code to handle effect vars.

r? `@compiler-errors` `@BoxyUwU`

Author: bors