feat(pack): add raw advertise refs and stateless protocol support

- Add raw flag to AdvertiseRefsRequest to enable raw pkt-line output
- Implement advertise_refs_raw function that calls git upload-pack/receive-pack with --advertise-refs
- Add stateless flag to GitProtocolFeatures for HTTP smart protocol support
- Modify upload_pack and receive_pack to accept stateless parameter
- Update command construction to include --stateless-rpc flag when enabled
- Add raw_data field to AdvertiseRefsResponse for raw output
- Update pack cache key computation to include raw service differentiation
- Initialize raw field to false in all request creation calls

pack/receive_pack.rs

@@ -14,8 +14,12 @@ impl GitBare {
     /// Client-streaming input → server-streaming output.
     /// Stdin packets are forwarded to the child process as they arrive from the client,
     /// while stdout is concurrently read and streamed back via a channel.
+    ///
+    /// `stateless` enables `--stateless-rpc` for HTTP smart protocol.
+    /// Leave `false` for SSH (persistent connection).
     pub async fn receive_pack(
         &self,
+        stateless: bool,
         input: impl tokio_stream::Stream<Item = Result<crate::pb::ReceivePackRequest, tonic::Status>>
         + Send
         + 'static,
@@ -23,6 +27,7 @@ impl GitBare {
         let bare_dir = self.bare_dir.to_string_lossy().into_owned();
         tracing::info!(
             repo = %bare_dir,
+            stateless = stateless,
             "spawning git receive-pack subprocess"
         );
 
@@ -31,11 +36,13 @@ impl GitBare {
         let stream = Box::pin(input);
         tokio::spawn(async move {
             let stream = stream;
-            let mut child = match Command::new("git")
-                .arg("--git-dir")
-                .arg(&bare_dir)
-                .arg("receive-pack")
-                .arg(&bare_dir)
+            let mut cmd = Command::new("git");
+            cmd.arg("--git-dir").arg(&bare_dir);
+            if stateless {
+                cmd.arg("--stateless-rpc");
+            }
+            cmd.arg("receive-pack").arg(&bare_dir);
+            let mut child = match cmd
                 .stdin(Stdio::piped())
                 .stdout(Stdio::piped())
                 .stderr(Stdio::piped())