Do not destroy plugin dialog on close, just hide it

[goanpeca]

This is handling the plugin dialog from this side, but maybe it would be better to handle it on the napari side, to avoid the creation of a duplicate dialog for some seconds.

I will open a PR on the napari side https://github.com/napari/napari/blob/f3b00c0936caaa87814e8c9b0497f20008d057e1/napari/_qt/_qapp_model/qactions/_plugins.py#L35C20-L35C37

To only create the dialog once. This however serves as POC so you can test how it works!

See how the counter keeps running between open and closing and how it remains on 406 after open and closing once it has finished.

[psobolewskiPhD]

Here's the napari PR:
napari/napari#6944

This feels really nice. Not sure where it's better for it to live.
@Czaki any thoughts?

[jaimergp]

I like this one better because getattr() is used in both approaches and that's still hacky. napari could have a public API for public references and that would be a cleaner solution, so for now let's go with this one but let's see if that public API lands sometime in the future.