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

[kavoc-brown]

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;
}