fix: #2016 Fix runtime, test templates and go codegen template

The go Runtime was confused about the EmprtyPredictionContext vs SIngletonPredictionContext.

For now, I have fixed up the go code for merge(), but I think longer term I will have to change the way the structures for
prediction context are organized, which is a piece of work that isn't worth it for v4.11. I will come back to that.