Add Qwen vision loading and Metal inference

src/engine/metal/qwen_mtplx/session_checkpoint.rs

@@ -27,6 +27,8 @@ pub(super) struct Identity {
 struct Manifest {
     identity: Identity,
     tag: [u8; 32],
+    #[serde(default)]
+    images: Vec<crate::engine::qwen_vision::Identity>,
     tokens: Vec<i32>,
     lazy_kv: bool,
     payload: serde_json::Value,
@@ -111,6 +113,7 @@ impl LiveSession {
             let manifest = serde_json::to_vec(&Manifest {
                 identity,
                 tag,
+                images: self.current_images.clone(),
                 tokens: saved.token_ids.clone(),
                 lazy_kv: saved.lazy_kv,
                 payload,
@@ -230,6 +233,8 @@ impl LiveSession {
         self.current = Some(saved);
         self.prefix = None;
         self.tag = manifest.tag;
+        self.current_images = manifest.images;
+        self.prefix_images.clear();
         Ok(true)
     }
 }
@@ -258,6 +263,8 @@ fn qwen_checkpoint_roundtrip_and_failed_restore_preserve_live_state() {
     .unwrap();
     let state = Some(State::Recurrent(vec![Some(leaf.clone()), None]));
     let mut live = LiveSession {
+        current_images: Vec::new(),
+        prefix_images: Vec::new(),
         current: Some(SessionSnapshot {
             token_ids: vec![1, 2, 3, 4],
             logits: leaf.clone(),