test: proptest property testing + cargo-fuzz fuzzing for donglora-cobs

crates/donglora-cobs/fuzz/fuzz_targets/fuzz_decode.rs

@@ -0,0 +1,9 @@
+//! Fuzz target: feed arbitrary bytes to decode(). Must never panic.
+#![no_main]
+use libfuzzer_sys::fuzz_target;
+
+fuzz_target!(|data: &[u8]| {
+    let mut buf = [0u8; 2048];
+    // Must not panic — may return None on invalid input.
+    let _ = donglora_cobs::decode(data, &mut buf);
+});