pyosys: rewrite using pybind11

- Rewrite all Python features to use the pybind11 library instead of boost::python.
  Unlike boost::python, pybind11 is a header-only library that is just included by Pyosys code, saving a lot of compile time on wheels.
- Factor out as much "translation" code from the generator into proper C++ files
- Fix running the embedded interpreter not supporting "from pyosys import libyosys as ys" like wheels
- Move Python-related elements to `pyosys` directory at the root of the repo
- Slight shift in bridging semantics:
  - Containers are declared as "opaque types" and are passed by reference to Python - many methods have been implemented to make them feel right at home without the overhead/ambiguity of copying to Python and then copying back after mutation
  - Monitor/Pass use "trampoline" pattern to support virual methods overridable in Python: virtual methods no longer require `py_` prefix
- Create really short test set for pyosys that just exercises basic functionality

misc/__init__.py

@@ -1,19 +0,0 @@
-import os
-import sys
-
-sys.setdlopenflags(os.RTLD_NOW | os.RTLD_GLOBAL)
-
-__dir__ = os.path.abspath(os.path.dirname(__file__))
-sys._pyosys_dir = os.path.abspath(__dir__)
-
-bin_ext = ".exe" if os.name == "nt" else ""
-
-_share_candidate = os.path.join(__dir__, "share")
-if os.path.isdir(_share_candidate):
-    sys._pyosys_share_dirname = _share_candidate + os.path.sep
-
-_abc_candidate = os.path.join(__dir__, f"yosys-abc{bin_ext}")
-if os.path.isfile(_abc_candidate):
-    sys._pyosys_abc = _abc_candidate
-
-__all__ = ["libyosys"]