Handle events from "initialSync" differently

Nobody has claimed this yet.

Is there a way to avoid differentiate events stemming from `matrixClient.startClient()` from other events? Specifically, I want to listen to "live events" to sometimes trigger application behavior when they come in.

However, I don't want the events from the initial sync to trigger that application behavior, since they are not "live".

I thought that `isInitialSyncComplete` would cover this use case, but if I understand the sequence correctly, `isInitialSyncComplete` is set independent of (typically before) the resulting events have been received.

I got things working "well enough" with this condition: `event.getLocalAge() > 5000` but it obviously relies on network conditions etc., so I was hoping to find a more fit for purpose solution using the SDK.

Start by tracing the event sequence around matrixClient.startClient() and isInitialSyncComplete, then compare it with the SDK's live-event handling. Define a fit-for-purpose way to distinguish initial-sync events from live events and verify that the distinction remains correct under varying network conditions.

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