This PR resolves a defeq diamond, which caused a problem in Mathlib:
```
import Mathlib
example (R : Type) [I : Ring R] :
@AddCommGroup.toGrindIntModule R (@Ring.toAddCommGroup R I) =
@Lean.Grind.Ring.instIntModule R (@Ring.toGrindRing R I) := rfl -- fails
```
This PR introduces `Lean.Grind.Field`, proves that a `IsCharP 0` field
satisfies `NoNatZeroDivisors`, and sets up some basic (currently
failing) tests for `grind`.
This PR splits `Lean.Grind.CommRing` into 4 typeclasses, for semirings
and noncommutative rings. This does not yet change the behaviour of
`grind`, which expects to find all 4 typeclasses. Later we will make
some generalizations.
This PR makes `#guard_msgs` to treat `trace` messages separate from
`info`, `warning` and `error`. It also introduce the ability to say
`#guard_msgs (pass info`, like `(drop info)` so far, and also adds
`(check info)` as the explicit form of `(info)`, for completeness.
Fixes#8266
