Revert "Stabilize `-Znext-solver=coherence`" This is a clean revert of #121848, prepared by running: ``` $ git revert17b322fa69-m1 ``` Which effectively reverts: *a138a92615,69fdd1457d,d93e047c9f,1a893ac648see: https://rust-lang.zulipchat.com/#narrow/stream/364551-t-types.2Ftrait-system-refactor/topic/nalgebra.20hang Closes #130056 r? lcnr