fix: consistent term order in linear integer normalization (#7560)

This PR ensures that we use the same ordering to normalize linear `Int`
terms and relations. This change affects `simp +arith` and `grind`
normalizer.

This consistency is important in the cutsat procedure. We want to avoid
a situation where the cutsat state contains both "atoms":
- `「(NatCast.natCast x + NatCast.natCast y) % 8」`
- `「(NatCast.natCast y + NatCast.natCast x) % 8」`

This was happening because we were using different orderings for
(nested) terms and relations (`=`, `<=`).

src/Lean/Meta/Tactic/Simp/Arith/Int/Basic.lean

@@ -211,7 +211,7 @@ def toLinearExpr (e : Expr) : MetaM (Int.Linear.Expr × Array Expr) := do
   if atoms.size == 1 then
     return (e, atoms)
   else
-    let (atoms, perm) := sortExprs atoms
+    let (atoms, perm) := sortExprs atoms (lt := false)
     let e := e.applyPerm perm
     return (e, atoms)
 

tests/lean/run/grind_cutsat_nat_dvd.lean

@@ -30,3 +30,15 @@ example (x y : Nat) :
 
 example (i : Nat) : i < 330 → 7 ∣ (660 + i) * (1319 - i) → 1319 - i < 1979 := by
   grind
+
+example (x y : Nat) (_ : 2 ≤ x) (_ : x ≤ 3) (_ : 2 ≤ y) (_ : y ≤ 3) :
+    4 ≤ (x + y) % 8 ∧ (x + y) % 8 ≤ 6 := by
+  grind
+
+example (x y : Nat) (_ : 2 ≤ x) (_ : x ≤ 3) (_ : 2 ≤ y) (_ : y ≤ 3) :
+    4 ≤ (y + x) % 8 ∧ (x + y) % 8 ≤ 6 := by
+  grind
+
+example (x y : Nat) (_ : 2 ≤ x) (_ : x ≤ 3) (_ : 2 ≤ y) (_ : y ≤ 3) :
+    4 ≤ (y + x) % 8 ∧ (y + x) % 8 ≤ 6 := by
+  grind