feat: add fuzz_urb_uac target

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

lib/fuzz/fuzz_targets/fuzz_urb_uac.rs

@@ -0,0 +1,21 @@
+#![no_main]
+
+use libfuzzer_sys::fuzz_target;
+use std::sync::Arc;
+use usbip_rs::mock::MockSocket;
+
+fuzz_target!(|data: &[u8]| {
+    let rt = tokio::runtime::Builder::new_multi_thread()
+        .enable_all()
+        .build()
+        .unwrap();
+    rt.block_on(async {
+        let device = usbip_rs::uac::build_uac_loopback_device().unwrap();
+
+        let mock = MockSocket::new(data.to_vec());
+        let output = mock.output_handle();
+        let _ = usbip_rs::handle_urb_loop(mock, Arc::new(device)).await;
+        let output_bytes = output.lock().unwrap();
+        usbip_rs::fuzz_helpers::assert_usbip_responses_valid(&output_bytes);
+    });
+});