Creating an explicit namespace with the same name as a callable breaks Python interop

[swernli]

From the Q# side, defining an explicit namespace in a cell with the same name as an earlier callable works because the two different entities are differentiable by type. But in Python interop, they try to occupy the same entity under qsharp.code and end up breaking the interop mechanisms:

We should decide what the Q# behavior and the Python interop expectation is in this situation. Does the later defined instance shadow the first? Should Q# disallow this?