Mixing two string models

### Summary

STRING_TYPE is a {i32, i8*} struct, but all string ops (+, ==, puts, casts) actually use i8*
standardize on i8* everywhere; drop STRING_TYPE.


### File Upload (optional)

_No response_

### Expected Results

-

### Actual Results

```console
-
```

### IRx version

```console
-
```

### Code of Conduct

- [x] I agree to follow the Code of Conduct