Investigate the performance of the iOS SDK vs the JS one

[funkyboy]

See project here
TLDR; JS SDK is faster in receiving/manning messages.

[funkyboy]

While having a debug or verbose logging level can be handy for developing, it introduces quite a overhead when measuring performance. In general we should be wary of measurements reported by customers when performed in debug mode.

On top of this I think our iOS SDK suffers of "unconditional logging". Meaning that some log statements are triggered regardless of the logLevel set in ARTClientOptions.
Measurements performed on this branch (and in particular with these changes) show that the roundtrip (sending and receiving from the server the same message, using local time as the exclusive reference point) for a message in iOS is around 80ms and is definitely comparable with the performance of the JS SDK, also around 80ms.

I will test these changes also to investigate this memory consumption issue, which I suspect is also affected by the uncontrolled logging mentioned above.

[funkyboy]

Fixed by #702