Allow video frame processing with push callbacks / delegates

## 🚀 Feature

Allow processing video frames with push callbacks or delegate instead of current poll / fetching

## Motivation & Examples

I explored demo and examples and I noticed is mot cases at least on iOS you have to schedule a timer to keep processing video frames at some requested interval. For applications that require minimum latency would be good to be able to process those video frames with some callback or delegate class. Ideally we could also specify dispatch queue where this processing would take place.

The motivation is to:
- minimise latency or
- reduce cpu usage in case scheduling timer at very low interval such as 1ms.
- simplify code so doesn't require each time doing some mutex locking mechanism.

The issue names no files, tests, or entry points. Start by locating the current video-frame polling or fetching path, then determine how a push callback or delegate and an optional dispatch queue should fit its API. Done means frames can be delivered through the new mechanism while preserving the existing processing behavior.

Written by the indexing model from the issue text.