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

tests/pyosys/run_tests.py

@@ -0,0 +1,39 @@
+from pathlib import Path
+import shutil
+import subprocess
+import sys
+
+__file_dir__ = Path(__file__).absolute().parent
+
+if len(sys.argv) != 2:
+	print(f"Usage: {sys.argv[0]} {sys.argv[1]}")
+	exit(64)
+
+binary = []
+if sys.argv[1] in ["yosys"]:
+	binary = [__file_dir__.parents[1] / "yosys", "-Qy"]
+else:
+	binary = [sys.argv[1]]
+
+tests = __file_dir__.glob("test_*.py")
+errors = False
+log_dir = __file_dir__ / "logs"
+try:
+	shutil.rmtree(log_dir)
+except FileNotFoundError:
+	pass
+for test in tests:
+	print(f"* {test.name} ", end="")
+	log_dir.mkdir(parents=True, exist_ok=True)
+	log = log_dir / (test.stem + ".log")
+	result = subprocess.run([
+		*binary,
+		test
+	], stdout=open(log, "w"), stderr=subprocess.STDOUT)
+	if result.returncode == 0:
+		print("OK!")
+	else:
+		print(f"FAILED: {log}")
+		errors = True
+if errors:
+	exit(1)