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

src/betterproto/__init__.py

@@ -779,6 +779,7 @@ class Message(ABC):
         """
         Get the binary encoded Protobuf representation of this message instance.
         """
+
         output = bytearray()
         for field_name, meta in self._betterproto.meta_by_field_name.items():
             try:
@@ -1002,6 +1003,14 @@ class Message(ABC):
         :class:`Message`
             The initialized message.
         """
+
+        if True:
+            # TODO: Make native deserialization optional
+
+            import betterproto_extras
+            betterproto_extras.deserialize(self, data)
+            return self
+
         # Got some data over the wire
         self._serialized_on_wire = True
         proto_meta = self._betterproto