fix: import LazyLock in on_media_cb hex-label unit test

PR #218 added a test using LazyLock without the local import that
other conn.rs tests use, causing cargo test and sanitizer jobs to fail
at compile time.

Co-authored-by: Alexander Wagner <info@alexanderwagnerdev.com>

Author: cursoragent

src/session/conn.rs

@@ -3674,6 +3674,8 @@ mod tests {
 
     #[test]
     fn on_media_cb_receives_hex_label_for_non_utf8_fourcc() {
+        use std::sync::{LazyLock, Mutex};
+
         static SEEN_CODEC: LazyLock<Mutex<Option<String>>> = LazyLock::new(|| Mutex::new(None));
         fn record_codec(_: u64, _: FrameType, codec: Option<&str>) -> bool {
             *SEEN_CODEC.lock().unwrap() = codec.map(str::to_owned);