Feature request: support `Enum`s in `inputMenu` and `inputChoice`

If I'm presenting a user with a list of choices, this works really nicely:

```
from pyinputplus import inputMenu

CHOICES = ('Go left', 'Go right')

inputMenu(choices=CHOICES, prompt='Pick a direction')
```

It would be really nice, however, to do this instead, which isn't supported:

```
from enum import Enum
from pyinputplus import inputMenu

class Choices(str, Enum):
one = 'Go left'
two = 'Go right'

inputMenu(choices=Choices, prompt='Pick a direction')
```

`Enum` classes are iterable, so will pass an `isinstance(, collections.abc.Iterable)` test. But they're not, strictly speaking, sequences, which means [this line](https://github.com/asweigart/pysimplevalidate/blob/98c17951be29689b5f5508c8ab9721dd44c55a9f/src/pysimplevalidate/__init__.py#L706) raises an error if I try to feed in an `Enum` of choices.

Would it be possible to support `Enum`s in `inputMenu` and `inputChoices`? I'd be happy to submit a PR if it would be helpful, but I don't know whether changing the validation function in `pysimplevalidate` would have unintended consequences.

Start with the validation logic in src/pysimplevalidate/__init__.py around line 706, then trace how pyinputplus inputMenu and inputChoice pass their choices to it. Confirm how Enum classes and their values should be accepted without changing existing sequence behavior, and verify both entry points with the examples in the issue.

Written by the indexing model from the issue text.