moonbit bindgen `s8`/`s16` lift corrupts values

```
package demo:poc;

interface api {
echo-s8: func(x: s8) -> s8;
echo-s16: func(x: s16) -> s16;
}

world exporter {
export api;
}

world runner {
import api;
export checksum: func() -> u32;
}
```