Make ControllerVector generic on a Controller

Currently, `ControllerVector` is:
```python
class ControllerVector(MutableMapping[int, Controller], BaseController):
```
Which presumibly would allow you to `add_sub_controller` with different types of `Controller`. Instead, we should make `ControllerVector` generic on a `Controller`.

## Acceptance Criteria
- `ControllerVector` is generic on a `Controller`
