message: Add assert to `as<int32_t>()` for dirty higher bits.
diff: @@ -67,6 +67,7 @@ constexpr int64_t Value::as<int64_t>() const noexcept
  template <>
  constexpr int32_t Value::as<int32_t>() const noexcept
  {
  + assert((i64 & 0xffffffff00000000) == 0);
  return static_cast<int32_t>(i64);
  }
  