Create python FFI with Py03

A python FFI that executes leo programs in memory similar to the Aleo SDK should be developed using the Py03 library. It should live in the Python SDK repository, but formally be imported as a separate python package.

Start in the Python SDK repository by reviewing its package entry points and existing Aleo SDK execution APIs. Clarify the intended Py03/PyO3 dependency and the boundary between the repository implementation and separately imported package. Done means a defined FFI that executes Leo programs in memory through the Python package.