Bootstrap DD3 Rust port workspace with host-first compatibility tests

fuzz/fuzz_targets/frame_decode.rs

@@ -0,0 +1,6 @@
+#![no_main]
+use libfuzzer_sys::fuzz_target;
+
+fuzz_target!(|data: &[u8]| {
+    let _ = dd3_protocol::decode_frame(data, dd3_protocol::MsgKind::AckDown as u8);
+});