CC Antoine for his expertise of the buffer protocol

Opaque Py_Buffer and PyObject structs will require a different approach and prevent some optimizations. The consumer will have to malloc() a Py_buffer struct on the heap. In non-trivial cases the producer (exporter) may have to malloc() another blob and store it in Py_buffer.internal [1]. I'm not particularly worried about the performance of malloc here.

[1] https://docs.python.org/3/c-api/buffer.html?highlight=pybuffer#c.Py_buffer.internal