Before a delegate is set, tracers provided are NoOp.
When a delegate is set, traces are provided from the delegate.
When a delegate is set after tracers have already been provided,
all tracers already provided will use the provided delegate implementation.
Tracer provider which provides ProxyTracers.
Before a delegate is set, tracers provided are NoOp. When a delegate is set, traces are provided from the delegate. When a delegate is set after tracers have already been provided, all tracers already provided will use the provided delegate implementation.