plt.pause uses removed `start_event_loop_default` API

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As the title suggests, attempting to pause through matplotlib currently raises an error. The minimum working example is:
```python
%matplotlib widget
from matplotlib import pyplot as plt

plt.plot([1,2,3])
plt.pause(1)
plt.plot([3,2,1])
plt.close()
```
This raises an attribute error trying to call FigureCanvasBase.start_event_loop_default. A little googling suggests this function has been removed since [version 3.0](https://matplotlib.org/api/api_changes.html#deprecated-apis).

Taking inspiration from #17, I guess the simplest get around is using time.sleep but is there a better solution?

Thanks for your help.

Start with the provided Jupyter example and trace plt.pause to the FigureCanvasBase.start_event_loop_default entry point mentioned in the report, using issue #17 for related context. Done means the example runs without the removed-API AttributeError and both plots can be displayed and closed as described.

Written by the indexing model from the issue text.