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/Cargo.toml

@@ -0,0 +1,12 @@
+[package]
+name = "betterproto-extras"
+version = "0.1.0"
+edition = "2021"
+
+[lib]
+name = "betterproto_extras"
+crate-type = ["cdylib"]
+
+[dependencies]
+prost-reflect = "0.11.4"
+pyo3 = { version = "0.19.0", features = ["abi3-py37", "extension-module"] }