Optimise Aethel search code

The search logic in `AethelQueryView.get()` works but is not fully optimized. Instead of doing this (in lines 106ff.)

```python
  # Check whether we have already added this sample for this result
  existing_sample = next(
      (s for s in result.samples if s.name == sample.name),
      None,
  )
```
it is worth investigating if we can keep track of the sample earlier in the `for` loop.