native/MASM divergence for `i64::checked_mul`

Reproduction requires #1140

```sh
cargo nextest run -p midenc-integration-tests \
--run-ignored all \
-E 'test(/checked_mul_i64_edge_case/)'
```

```
thread 'end_to_end::arithmetic::checked_mul_i64_edge_cases' (188951) panicked at tests/integration/src/end_to_end/arithmetic.rs:1082:13:
Found minimal(shrinked) failing case: (-4611686018427387904, 2)
Failure: Reason("assertion failed: `(left == right)` \n left: `[0, 0, 0, 0, 0, 0, 0, 128, 1]`, \n right: `[0, 0, 0, 0, 0, 0, 0, 128, 0]`: VM output mismatch at tests/integration/src/end_to_end/arithmetic.rs:1075")
```

失敗的測試位於 tests/integration/src/end_to_end/arithmetic.rs 第 1082 行。執行提供的 cargo nextest 命令，以重現 i64::checked_mul 在輸入 (-4611686018427387904, 2) 時原生實作與 MASM 實作之間的差異。檢查編譯器針對帶檢查的乘法運算的程式碼生成，重點關注 64 位元整數的溢位處理。

由索引模型根據 Issue 內容生成。