Loggable currently builds messages eagerly, even if the message won't be emitted because of the logger's level setting. This is particularly bad because `log_inspect` uses `respond_to?` on every operation to be logged, which walks the Ruby module tree, which is slow and bad.

https://github.com/cheald/mongo-ruby-driver/commit/e187ab023d01ec256a3142053e23a12360af8f92

Using the same benchmark as my previous code, this improved my benchmark runtime by a full 10% (12.1 sec -> 10.9 sec).