NRE on OperationBuilderPool.Get() for NOOP

Using the NBomber test referenced in NCBC-3161, after updating to the latest CouchbaseNetClient master (as of 2022-03-17 1:51 PDT SHA = d0ff608524508e24c2cb0f08fd380d4c8101137d), long runs of the tool will hit an NRE at 

var builder = OperationBuilderPool.Get(); 

in OperationBase.cs: SendAsync()

This implies that OperationConfiguration.Configure() is being called in a thread-unsafe way without proper synchronization.