LastOpFixer currently can only be constructed with a Namespace. For bulkWrite we want to be able to construct it without a Namespace so we only have to use one object for the entire write which can take place across multiple namespaces. For bulkWrite we would like to move this instantiation into performWrites

A couple ways this could be done

make a ctor that allows us to set isLocalDB directly. Unless all namespaces used in a bulkWrite are local, otherwise isLocalDB should be false and we should set lastOp correctly for no-op writes on replicated namespaces

let startingOp() take in a namespace/bool indicating whether it is a local write, if it is, then we make the startingOp() and finishedOpSuccessfully() pair no-op for that particular write