BmiJulia easier to subclass.

To subclass the BmiJulia class you now have to something like

```python
class WflowBmi(BmiJulia):
def __init__(self):
m = self.from_name("Wflow.Model", implementation_name="Wflow.BMI")
super().__init__(m.model, m.implementation)
```

See https://github.com/eWaterCycle/grpc4bmi/pull/144/files#r1374200483

It would be nicer if you could do

```
class WflowBmi(BmiJulia):
def __init__(self):
super().__init__("Wflow.Model", "Wflow.BMI")
```

Con: this makes __init__ fat as it needs to call julia code +