This PR improves the counterexamples produced by `grind linarith` for
`NatModule`s. `grind` now hides occurrences of the auxiliary function
`Grind.IntModule.OfNatModule.toQ`.
This PR adds support for `NatModule` equalities and inequalities in
`grind linarith`. Examples:
```lean
open Lean Grind Std
example [NatModule α] [LE α] [LT α]
[LawfulOrderLT α] [IsLinearOrder α] [OrderedAdd α]
(x y : α) : x ≤ y → 2 • x + y ≤ 3 • y := by
grind
example [NatModule α] [AddRightCancel α] [LE α] [LT α]
[LawfulOrderLT α] [IsLinearOrder α] [OrderedAdd α]
(a b c d : α) : a ≤ b → a ≥ c + d → d ≤ 0 → d ≥ 0 → b = c → a = b := by
grind
```
This PR implements the infrastructure for supporting `NatModule` in
`grind linarith` and uses it to handle disequalities. Another PR will
add support for equalities and inequalities. Example:
```lean
open Lean Grind
variable (M : Type) [NatModule M] [AddRightCancel M]
example (x y : M) : 2 • x + 3 • y + x = 3 • (x + y) := by
grind
```
