assistant2: Improve Lua script rendering (#26389)

This PR improves the rendering of Lua scripts provided to the scripting
tool.

We now render them in code blocks with syntax highlighting:

<img width="1297" alt="Screenshot 2025-03-10 at 2 40 51 PM"
src="https://github.com/user-attachments/assets/def65b5c-86a8-490f-aaa5-5cc1687fe01e"
/>

Release Notes:

- N/A

crates/assistant2/src/tool_use.rs

@@ -202,7 +202,7 @@ impl ToolUseState {
         &mut self,
         tool_use_id: LanguageModelToolUseId,
         output: Result<String>,
-    ) {
+    ) -> Option<PendingToolUse> {
         match output {
             Ok(output) => {
                 self.tool_results.insert(
@@ -213,7 +213,7 @@ impl ToolUseState {
                         is_error: false,
                     },
                 );
-                self.pending_tool_uses_by_id.remove(&tool_use_id);
+                self.pending_tool_uses_by_id.remove(&tool_use_id)
             }
             Err(err) => {
                 self.tool_results.insert(
@@ -228,6 +228,8 @@ impl ToolUseState {
                 if let Some(tool_use) = self.pending_tool_uses_by_id.get_mut(&tool_use_id) {
                     tool_use.status = PendingToolUseStatus::Error(err.to_string().into());
                 }
+
+                self.pending_tool_uses_by_id.get(&tool_use_id).cloned()
             }
         }
     }