add protobuf transport and refactor to support (#24)

proto/messages.proto

@@ -0,0 +1,29 @@
+syntax = "proto3";
+
+package djls;
+
+// Commands we send to Python
+message ToAgent {
+  oneof command {
+    HealthCheck health_check = 1;
+    Shutdown shutdown = 2;
+  }
+}
+
+message HealthCheck {}
+message Shutdown {}
+
+// Responses we get back
+message FromAgent {
+  oneof message {
+    HealthCheckResponse health_check = 1;
+    Error error = 2;
+  }
+}
+
+message HealthCheckResponse {}
+
+message Error {
+  string message = 1;
+  string traceback = 2;  // Optional stack trace from Python
+}