Preserve raw response usage metadata (#41980)

## What changed

- Include the complete upstream `response.usage` object in
  `ResponseUsageMetadata.metadata` while retaining the existing `amount` field.
- Expose the metadata through `rawResponse/completed` notifications and update
  the generated JSON and TypeScript schemas.

## Testing

- Cover SSE, WebSocket, turn, and compaction completion paths.

GitOrigin-RevId: 6d79b1b4c92ac11abf43ec98f380b4868288a701

codex-rs/app-server-protocol/src/protocol/v2/thread.rs

@@ -1856,12 +1856,14 @@ pub struct RawResponseCompletedNotification {
 #[ts(export_to = "v2/")]
 pub struct ResponseUsageMetadata {
     pub amount: Option<String>,
+    pub metadata: Option<JsonValue>,
 }
 
 impl From<codex_protocol::ResponseUsageMetadata> for ResponseUsageMetadata {
     fn from(value: codex_protocol::ResponseUsageMetadata) -> Self {
         Self {
             amount: value.amount,
+            metadata: value.metadata,
         }
     }
 }