Generic typing of create namespace ops is broken

The create namespace has several ops that use generics in unsafe and invalid ways. Whenever possible, it is best for methods which returns objects with generic parameters to accept method arguments that also specify those types. Otherwise, the compiler has a hard time guaranteeing that those generic type parameters will be fulfilled as expected.

There are also some places that use `T extends NativeType` and others that use `T` and others that use `T extends IntegerType`, all of which are distinct—but then these `T`s are mixed and matched in invalid ways.