I just tried your project this morning, and I can get the base CS generated code to work properly.
It seems like he doesn't find the Namespace you're using at the top of your files

I assume that all the missing types are coming from this namespace but I dont know where to find it.

Thanks for the help you can bring me, nice project btw :)

My configuration.php is as provided and everything else is as provided other than changes on .twig.

inside WRITE_TYPE_MAPPER there are the Writing method for every varType listed. Although based on tests I did the generator doesn't ever generate writeUInt, writeVarInt, writeVarShort, writeVarUShort as the methods. It always uses the first Method listed on the Config.

based on testing there is something wrong with this call " $this->writeMethod = MethodMappingHelper::getMethod('write_method', $object);"