Stats will not get emitted as MediaWiki::emitBufferedStatsdData is never called for the PerDbName factory.

Possible solutions:

• When emitting events for the default StatsdDataFactory, also emit for the PerDbName factory
• Instead create a wrapper class implementing StatsdDataFactoryInterface that takes the extra prefix to be added to metrics, resulting in a single buffering factory for stats to be emitted from, something like "PrefixingStatsdDataFactoryProxy"

The PerDbName factory was initially introduced in https://gerrit.wikimedia.org/r/#/c/443467/