Implement `__contains__` for `timeseries.Bounds` and `timeseries.SystemBounds`

### What's needed?

It would be nice to be able to write:

```py
if value in bounds:
    do_something(value)
else:
    raise OutOfBounds(value)
```

### Proposed solution

Implement [`__contains__()`](https://docs.python.org/3/reference/datamodel.html#object.__contains__) for both classes.