Wire the PatchUpdated events through app_server (#18289)

Wires patch_updated events through app_server. These events are parsed
and streamed while apply_patch is being written by the model. Also adds 500ms of buffering to the patch_updated events in the diff_consumer.

The eventual goal is to use this to display better progress indicators in
the codex app.

codex-rs/app-server-protocol/schema/json/ServerNotification.json

@@ -993,6 +993,32 @@
       ],
       "type": "object"
     },
+    "FileChangePatchUpdatedNotification": {
+      "properties": {
+        "changes": {
+          "items": {
+            "$ref": "#/definitions/FileUpdateChange"
+          },
+          "type": "array"
+        },
+        "itemId": {
+          "type": "string"
+        },
+        "threadId": {
+          "type": "string"
+        },
+        "turnId": {
+          "type": "string"
+        }
+      },
+      "required": [
+        "changes",
+        "itemId",
+        "threadId",
+        "turnId"
+      ],
+      "type": "object"
+    },
     "FileUpdateChange": {
       "properties": {
         "diff": {
@@ -4668,6 +4694,26 @@
       "title": "Item/fileChange/outputDeltaNotification",
       "type": "object"
     },
+    {
+      "properties": {
+        "method": {
+          "enum": [
+            "item/fileChange/patchUpdated"
+          ],
+          "title": "Item/fileChange/patchUpdatedNotificationMethod",
+          "type": "string"
+        },
+        "params": {
+          "$ref": "#/definitions/FileChangePatchUpdatedNotification"
+        }
+      },
+      "required": [
+        "method",
+        "params"
+      ],
+      "title": "Item/fileChange/patchUpdatedNotification",
+      "type": "object"
+    },
     {
       "properties": {
         "method": {