Native deserialization based on Rust and PyO3

Proof of concept
Only capable of deserializing (nested) Messages with primitive fields
No handling of lists, maps, enums, .. implemented yet
See `example.py` for a working example

betterproto-extras/pyproject.toml

@@ -0,0 +1,16 @@
+[build-system]
+requires = ["maturin>=1.2,<2.0"]
+build-backend = "maturin"
+
+[project]
+name = "betterproto-extras"
+requires-python = ">=3.7"
+classifiers = [
+    "Programming Language :: Rust",
+    "Programming Language :: Python :: Implementation :: CPython",
+    "Programming Language :: Python :: Implementation :: PyPy",
+]
+
+
+[tool.maturin]
+features = ["pyo3/extension-module"]