fix: resolve type mismatch in async item stream handling

Co-authored-by: aider (openai/andrew/openrouter/deepseek/deepseek-chat-v3.1) <aider@aider.chat>

src/services/async_item_service.rs

@@ -243,15 +243,16 @@ impl AsyncItemService {
         let limited_stream = if length > 0 {
             // We need to track how many bytes we've sent
             let mut bytes_sent = 0;
-            Box::pin(stream.take_while(move |result| {
+            let limited = stream.take_while(move |result| {
                 if bytes_sent >= length {
-                    return false;
+                    return std::future::ready(false);
                 }
                 if let Ok(chunk) = result {
                     bytes_sent += chunk.len() as u64;
                 }
-                true
-            }))
+                std::future::ready(true)
+            });
+            Box::pin(limited)
         } else {
             Box::pin(stream)
         };