### `read_bytes`

It's not safe to return `bytearray` when we think it's `bytes`
```python
a = rom.read_bytes(8, 3)
hash(a)  # This won't crash, right?
```

### `write_bytes`

`Iterable[SupportsIndex]` is what's required for `bytearray.__setitem__(slice, values)`
We need to add `__len__` for the `len(values)` in this function.

…nto localrom-typing