8285: Don't recheck obligations if we have learned nothing new r=matklad a=flodiebold
This is just the most trivial check: If no inference variables have been updated, and there are no new obligations, we can just skip trying to solve them again. We could be smarter about it, but this already helps quite a bit, and I don't want to touch this too much before we replace the inference table by Chalk's.
Fixes#8263 (well, improves it quite a bit).
Co-authored-by: Florian Diebold <flodiebold@gmail.com>
00ce7ae524