add type annotation

[mazlum]

Do you think adding type annotation completely?

[sebastian-philipp]

what do you miss exacly? Together with django-stubs, this is already super helpful as it is.

[mazlum]

There is no type annotation for some functions.

https://github.com/makinacorpus/django-safedelete/blob/master/safedelete/queryset.py#L98

And the latest versions of mypy and django-stubs say: "call to untyped function in typed context"

for .filter function.

[Gagaro]

The idea was to just add the minimum so that mypy could be used with safedelete, but I added a few typings at the same time to bootstrap it.

Feel free to open a PR to add more if you feel like it, I don't think I'll have time to do that anytime soon.