[PyCDE] Investigate using pybind11 without the C API

[teqdruid]

Going through a C API is a PITA so I'm more likely to add features in Python than CIRCT. That's unfortunate since at least several things are re-useable and really should be in CIRCT's C++ code. As of now, PyCDE has this awkward one-foot-in-each-world situation.

@stellaraccident: now that we have universal builds, do you think we'll run into linking issues? If so, would it be easy(-ish) to cram all the problematic code into the PyBind11 extension SO to really avoid them? That would work for the PyCDE use case.