don't update when nothing changed
don't update when nothing changed

Summary:
The QPL plugin is sending the current time on the device every second, this was causing state updates every second.

QPL: don't update the state, when we did not receive new traces.
Client: only dispatch the update event, when the new state is different from the current.

Reviewed By: passy

Differential Revision: D12956337

fbshipit-source-id: c006540097408ead8fb8c5aac3aaaa220c1a3951

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