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

setup.py

@@ -16,18 +16,19 @@ import os
 import re
 import shlex
 import shutil
+from pathlib import Path
 from setuptools import setup, Extension
-from setuptools.command.build_ext import build_ext
 
-__dir__ = os.path.dirname(os.path.abspath(__file__))
+import pybind11
+from pybind11.setup_helpers import build_ext
+
+__yosys_root__ = Path(__file__).parent
 
 yosys_version_rx = re.compile(r"YOSYS_VER\s*:=\s*([\w\-\+\.]+)")
 
-version = yosys_version_rx.search(
-    open(os.path.join(__dir__, "Makefile"), encoding="utf8").read()
-)[1].replace(
-    "+", "."
-)  # Convert to patch version
+with open(__yosys_root__ / "Makefile", encoding="utf8") as f:
+    # Extract and convert + to patch version
+    version = yosys_version_rx.search(f.read())[1].replace("+", ".")
 
 
 class libyosys_so_ext(Extension):
@@ -38,7 +39,13 @@ class libyosys_so_ext(Extension):
             "libyosys.so",
             [],
         )
+
+        # when iterating locally, you probably want to set this variable
+        # to avoid mass rebuilds bec of pybind11's include path changing
+        pybind_include = os.getenv("_FORCE_PYBIND_INCLUDE", pybind11.get_include())
+
         self.args = [
+            f"PYBIND11_INCLUDE={pybind_include}",
             "ENABLE_PYOSYS=1",
             # Would need to be installed separately by the user
             "ENABLE_TCL=0",
@@ -73,22 +80,23 @@ class libyosys_so_ext(Extension):
                 *self.args,
             ]
         )
-        build_path = os.path.dirname(os.path.dirname(bext.get_ext_fullpath(self.name)))
-        pyosys_path = os.path.join(build_path, "pyosys")
+        ext_fullpath = Path(bext.get_ext_fullpath(self.name))
+        build_path = ext_fullpath.parents[1]
+        pyosys_path = build_path / "pyosys"
         os.makedirs(pyosys_path, exist_ok=True)
 
         # libyosys.so
-        target = os.path.join(pyosys_path, os.path.basename(self.name))
+        target = pyosys_path / self.name
         shutil.copy(self.name, target)
-        bext.spawn(["strip", "-S", target])
+        bext.spawn(["strip", "-S", str(target)])
 
         # yosys-abc
-        yosys_abc_target = os.path.join(pyosys_path, "yosys-abc")
+        yosys_abc_target = pyosys_path / "yosys-abc"
         shutil.copy("yosys-abc", yosys_abc_target)
-        bext.spawn(["strip", "-S", yosys_abc_target])
+        bext.spawn(["strip", "-S", str(yosys_abc_target)])
 
         # share directory
-        share_target = os.path.join(pyosys_path, "share")
+        share_target = pyosys_path / "share"
         try:
             shutil.rmtree(share_target)
         except FileNotFoundError:
@@ -104,14 +112,16 @@ class custom_build_ext(build_ext):
         return ext.custom_build(self)
 
 
+with open(__yosys_root__ / "README.md", encoding="utf8") as f:
+    long_description = f.read()
+
 setup(
     name="pyosys",
     packages=["pyosys"],
     version=version,
     description="Python access to libyosys",
-    long_description=open(os.path.join(__dir__, "README.md")).read(),
+    long_description=long_description,
     long_description_content_type="text/markdown",
-    install_requires=["wheel", "setuptools"],
     license="MIT",
     classifiers=[
         "Programming Language :: Python :: 3",
@@ -119,7 +129,6 @@ setup(
         "Operating System :: POSIX :: Linux",
         "Operating System :: MacOS :: MacOS X",
     ],
-    package_dir={"pyosys": "misc"},
     python_requires=">=3.8",
     ext_modules=[libyosys_so_ext()],
     cmdclass={