Add reset_function callback option

[hoggatt]

Add a callback function that can be run in the case of a reset.

This is useful if you want to change some value in your app in the case of a reset. Pulling from my fork that, unfortunately, I have so it won't let me make a pull request.

To the main function add this argument:
reset_function: Callable[[], None] = None,

With this doc string:

reset_function (Callable[[], None], optional):
    Function that is called after the user has reset the combobox. Defaults to None.

Then this needs to be in the if interaction == "reset": block, before the return:

if reset_function is not None:
    reset_function()

[hoggatt]

Here is the docstring in the readme:

---

reset_function: Callable[[], None] = None

Function that will be called when the combobox is reset.

[m-wrzr]

Thanks for the input! I'll add it to the next version 👍 #59