Explicitly use u64 operations for safe u8 arithmetic

Fixes #5449

Without this fix, because we use `u8` load and store instructions,
the overflow check (which relies on `u64` arithmetic) gets nullified.

sway-lib-core/src/ops.sw

@@ -81,11 +81,22 @@ impl Add for u16 {
 
 impl Add for u8 {
     fn add(self, other: Self) -> Self {
-        let res = __add(self, other);
-        if __gt(res, Self::max()) {
+        let self_u64 = asm(input: self) {
+            input: u64
+        };
+        let other_u64 = asm(input: other) {
+            input: u64
+        };
+        let res_u64 = __add(self_u64, other_u64);
+        let max_u8_u64 = asm(input: Self::max()) {
+            input: u64
+        };
+        if __gt(res_u64, max_u8_u64) {
             __revert(0)
         } else {
-            res
+            asm(input: res_u64) {
+                input: u8
+            }
         }
     }
 }
@@ -239,11 +250,22 @@ impl Multiply for u16 {
 
 impl Multiply for u8 {
     fn multiply(self, other: Self) -> Self {
-        let res = __mul(self, other);
-        if __gt(res, Self::max()) {
+        let self_u64 = asm(input: self) {
+            input: u64
+        };
+        let other_u64 = asm(input: other) {
+            input: u64
+        };
+        let res_u64 = __mul(self_u64, other_u64);
+        let max_u8_u64 = asm(input: Self::max()) {
+            input: u64
+        };
+        if __gt(res_u64, max_u8_u64) {
             __revert(0)
         } else {
-            res
+            asm(input: res_u64) {
+                input: u8
+            }
         }
     }
 }

test/src/e2e_vm_tests/test_programs/should_fail/arith_overflow/u8_add_overflow/test.toml

@@ -1,3 +1,3 @@
-category = "disabled"
+category = "run"
 expected_result = { action = "revert", value = 0 }
 validate_abi = false

test/src/e2e_vm_tests/test_programs/should_fail/arith_overflow/u8_mul_overflow/test.toml

@@ -1,3 +1,3 @@
-category = "disabled"
+category = "run"
 expected_result = { action = "revert", value = 0 }
 validate_abi = false