Can we refer to spanTimeoutTimers property instead of accessing ivar directly?

Actually, I think we can just ditch the timers all together by utilizing dispatch_after.
We can also introduce another callback that will be called whenever a span ceases to exist. As of now, we only update SpanStackingHandler when a span is deallocated without getting closed in some way. Perhaps we can expand this?

Adding a new callback will require more work but it will save us the overhead of dispatching an operation every time a span is created

I'm going to raise a separate task to implement these optimizations at a later date

1. This results in the spansByName being cleared every time the plugin gets installed. It shouldn't matter as the plugin will presumably be installed once. It's an unnecessary side effect though
2. NSMutableDictionary proved to be not efficient enough for our purposes in the past. As this will be heavily used, I think we should opt for an std::map

2. Given that the keys to this NSMutableDictionary are strings, changing it to a C++ map will either carry an encode/decode overhead (to go from NSString (UTF-16) <-> std::string (UTF-8) or will require that we implement a custom std::hash and std::equal_to so that we can directly store the NSString*s in the C++ map.

I think we should keep the existing NSMutableDictionary implementation until we have a chance to benchmark the performance differences between the implementations.

Adding a new callback will require more work but it will save us the overhead of dispatching an operation every time a span is created