trait solver: Resolve region vars in max universe Fixes rust-lang/rust#157862 The ICE comes from computing the max universe of a region constraint after a region var has already been unified with something else. In that state, asking universe_of_lt directly can hit None and panic. This makes the region visitor opportunistically resolve ReVars first, then inspect the resolved region. Type and const infer vars stay as-is because this path already bails on non-region inference before it needs more structure from them.