Further increase performance of DIGraph in production by not needing override feature

[levibostian]

The DIGraph is auto-generated. The graph that's generated today is great except 1 thing I would like to improve.

The production and testing graph are identical. The graph contains this feature that allows you to override an instance in the graph which is used to provide a mock for testing. This override feature has a performance hit because it uses a mutex. Ideally, you don't need this feature in production, just testing. It would be great if the production graph didn't include this feature to make it even more performant at runtime.

Be sure that whatever solution is chosen does not introduce side effects into the test suite. The test suite should continue to be easy to use.