It improves compile time in `--release` mode quite a bit, it doesn't
really slow things down and, conceptually, it seems closer to what we
want the physical architecture to look like (we don't want to
monomorphise EVERYTHING in a single leaf crate).
This adds some tools helpful when debugging nondeterminism in analysis-stats:
- a `--randomize` option that analyses everything in random order
- a `-vv` option that prints even more detail
Also add a debug log if Chalk fuel is exhausted (which would be a source of
nondeterminism, but didn't happen in my tests).
I found one source of nondeterminism (rust-lang/chalk#331), but there are still
other cases remaining.
It's not very different, except we can directly use Salsa IDs instead of casting
them. This means we need to refactor the handling of errors to get rid of
UNKNOWN_TRAIT though.
