perf(vm): in-place compare ops + Int-Int fast path

Mirror the treatment LessEqual already got onto Equal/NotEqual/Less/
Greater/GreaterEqual — rewrite sp directly, check the type tag for
Int==Int in the hot branch, short-circuit to cachedTrue/cachedFalse
without a second method call. Keeps the slow fallback for mixed /
string / date types.

Bench movement is minor on SQL paths (WHERE is already pcode and
skips these ops); the win is on PRG comparisons that cache-miss out
of the pcode path — FOR-condition short forms, IF chains, etc.

Verification
 - go test ./...              ALL PASS
 - FiveSql2 test_sql1999      43/43
 - tests/compat_harbour       56/56

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

hbrt/ops_compare.go

@@ -22,9 +22,26 @@ import "strings"
 // Equal pops two values, pushes boolean result.
 // Harbour: hb_vmEqual (hvm.c:3974)
 func (t *Thread) Equal() {
-	b := t.pop()
-	a := t.pop()
-	t.push(MakeBool(valueEqual(a, b)))
+	t.sp -= 2
+	a := t.stack[t.sp]
+	b := t.stack[t.sp+1]
+	t.stack[t.sp+1] = cachedNil
+	// Fast path: Int == Int
+	if a.Type() == tInt && b.Type() == tInt {
+		if int64(a.scalar) == int64(b.scalar) {
+			t.stack[t.sp] = cachedTrue
+		} else {
+			t.stack[t.sp] = cachedFalse
+		}
+		t.sp++
+		return
+	}
+	if valueEqual(a, b) {
+		t.stack[t.sp] = cachedTrue
+	} else {
+		t.stack[t.sp] = cachedFalse
+	}
+	t.sp++
 }
 
 // ExactEqual pops two values, pushes boolean result.
@@ -37,9 +54,25 @@ func (t *Thread) ExactEqual() {
 
 // NotEqual pops two values, pushes boolean result.
 func (t *Thread) NotEqual() {
-	b := t.pop()
-	a := t.pop()
-	t.push(MakeBool(!valueEqual(a, b)))
+	t.sp -= 2
+	a := t.stack[t.sp]
+	b := t.stack[t.sp+1]
+	t.stack[t.sp+1] = cachedNil
+	if a.Type() == tInt && b.Type() == tInt {
+		if int64(a.scalar) != int64(b.scalar) {
+			t.stack[t.sp] = cachedTrue
+		} else {
+			t.stack[t.sp] = cachedFalse
+		}
+		t.sp++
+		return
+	}
+	if !valueEqual(a, b) {
+		t.stack[t.sp] = cachedTrue
+	} else {
+		t.stack[t.sp] = cachedFalse
+	}
+	t.sp++
 }
 
 // --- Relational operators ---
@@ -47,13 +80,29 @@ func (t *Thread) NotEqual() {
 // Less pops two values, pushes boolean result.
 // Harbour: hb_vmLess (hvm.c:4176)
 func (t *Thread) Less() {
-	b := t.pop()
-	a := t.pop()
+	t.sp -= 2
+	a := t.stack[t.sp]
+	b := t.stack[t.sp+1]
+	t.stack[t.sp+1] = cachedNil
+	if a.Type() == tInt && b.Type() == tInt {
+		if int64(a.scalar) < int64(b.scalar) {
+			t.stack[t.sp] = cachedTrue
+		} else {
+			t.stack[t.sp] = cachedFalse
+		}
+		t.sp++
+		return
+	}
 	cmp, ok := valueCompare(a, b)
 	if !ok {
 		panic(t.argError("<", a, b))
 	}
-	t.push(MakeBool(cmp < 0))
+	if cmp < 0 {
+		t.stack[t.sp] = cachedTrue
+	} else {
+		t.stack[t.sp] = cachedFalse
+	}
+	t.sp++
 }
 
 // LessEqual pops two values, pushes boolean result.
@@ -86,24 +135,56 @@ func (t *Thread) LessEqual() {
 
 // Greater pops two values, pushes boolean result.
 func (t *Thread) Greater() {
-	b := t.pop()
-	a := t.pop()
+	t.sp -= 2
+	a := t.stack[t.sp]
+	b := t.stack[t.sp+1]
+	t.stack[t.sp+1] = cachedNil
+	if a.Type() == tInt && b.Type() == tInt {
+		if int64(a.scalar) > int64(b.scalar) {
+			t.stack[t.sp] = cachedTrue
+		} else {
+			t.stack[t.sp] = cachedFalse
+		}
+		t.sp++
+		return
+	}
 	cmp, ok := valueCompare(a, b)
 	if !ok {
 		panic(t.argError(">", a, b))
 	}
-	t.push(MakeBool(cmp > 0))
+	if cmp > 0 {
+		t.stack[t.sp] = cachedTrue
+	} else {
+		t.stack[t.sp] = cachedFalse
+	}
+	t.sp++
 }
 
 // GreaterEqual pops two values, pushes boolean result.
 func (t *Thread) GreaterEqual() {
-	b := t.pop()
-	a := t.pop()
+	t.sp -= 2
+	a := t.stack[t.sp]
+	b := t.stack[t.sp+1]
+	t.stack[t.sp+1] = cachedNil
+	if a.Type() == tInt && b.Type() == tInt {
+		if int64(a.scalar) >= int64(b.scalar) {
+			t.stack[t.sp] = cachedTrue
+		} else {
+			t.stack[t.sp] = cachedFalse
+		}
+		t.sp++
+		return
+	}
 	cmp, ok := valueCompare(a, b)
 	if !ok {
 		panic(t.argError(">=", a, b))
 	}
-	t.push(MakeBool(cmp >= 0))
+	if cmp >= 0 {
+		t.stack[t.sp] = cachedTrue
+	} else {
+		t.stack[t.sp] = cachedFalse
+	}
+	t.sp++
 }
 
 // --- Logical operators ---