Feature request: add an event handler on event source received

## Problem
At the moment the SDK provides realtime capabilities through `eventSourceUrl` and `realtime` init parameters but it doesn't expose a specific handler when a new event is received.
To add custom logic, it requires to setup the event-source manually

## Solution
A solution could be to add a new handler `onEventSourceReceived` that would be triggered when a new event is received to allow for additional logic independently from `onChange`

Start by locating the SDK entry points that process the eventSourceUrl and realtime initialization parameters, then compare that flow with the existing onChange handling. Confirm how manually configured event sources deliver events. Done means exposing an onEventSourceReceived handler that runs for each received event independently of onChange, with coverage for the new behavior.

Written by the indexing model from the issue text.