Bug on async Events methods

The `async def prev(self, count=None)` and `async def next(self, count=None)` methods on [client/viscera/events.py](https://github.com/canonical/python-libmaas/blob/0.6.8/maas/client/viscera/events.py) are not using `await` when calling `self._fetch`, which is causing errors when the async iterator tries to continue reading events of a previous/next page.

How to reproduce:
```python
events = await client.events.query()

async for e in events.forwards():
print(e.event_id, e.event_type)
```

The snippet above will fetch some events and then throw an error:
```
...
1902 Performing PXE boot
1906 Loading ephemeral
1907 Image Deployed
1909 Deployed

Traceback (most recent call last):
File "/maas_tests/env/lib/python3.13/site-packages/maas/client/viscera/events.py", line 259, in __anext__
return next(self._current_iter)
StopIteration

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
File "/maas_tests/env/lib/python3.13/site-packages/marimo/_runtime/executor.py", line 115, in execute_cell_async
await eval(cell.body, glbls)
Cell marimo://test-python-libmaas.py#cell=cell-17, line 3, in
async for e in events.forwards():
print(e.event_id, e.event_type)
File "/maas_tests/env/lib/python3.13/site-packages/maas/client/viscera/events.py", line 262, in __anext__
self._current_iter = reversed(self._current)
~~~~~~~~^^^^^^^^^^^^^^^
TypeError: 'coroutine' object is not reversible
```

To fix, we just need to add `await` to the following lines:
- https://github.com/canonical/python-libmaas/blob/0.6.8/maas/client/viscera/events.py#L169
- https://github.com/canonical/python-libmaas/blob/0.6.8/maas/client/viscera/events.py#L180

Comienza en maas/client/viscera/events.py, en los métodos asíncronos prev y next mencionados en las líneas 169 y 180, y luego reproduce el problema con el ejemplo proporcionado de iteración asíncrona events.forwards(). Se considera terminado cuando iterar por las páginas de eventos ya no produce un objeto coroutine ni el TypeError indicado.

Escrito por el modelo de indexación a partir del texto del issue.