Support for `BGContinuedProcessingTask` on iOS 26+

[szw0407]

It is proper to add support for long running background tasks (e.g., ML inference). Personally I think it is really similar to what Android foreground tasks can do.

[szw0407]

I have forked the project and tried some modifications. If it makes sense, I shall add some update or descriptions.

[Haltarys]

Interested in this being supported as well!