revisit logging system

[pgautier404]

Using a static log provider with a logger factory supplied by the clients isn't going to work in a multi-client environment (e.g., I construct a cache client to create a cache and a topic client to pubsub on it). We need to adjust the current logic to make sure clients don't clobber one another's logging. The python SDK looks like a good candidate for comparing approaches, as it also uses a static logger.

[anitarua]

Apple's Logger is for iOS 14+ but it seems like we might be able to use the swift-log library instead of writing our own custom LogProvider class as we had been doing. Currently investigating