fix: Close HttpClient in StreamingDataSource.stop() to prevent resource leak

- Add close() method to HttpClient class that closes underlying http.Client
- Call _pollingClient.close() in StreamingDataSource.stop() method
- Fixes dart analyzer error about unclosed HttpClient resource

Addresses Bugbot finding about resource leak.

Co-Authored-By: [email protected] <[email protected]>

Author: devin-ai-integration[bot]

packages/common/lib/src/network/http_client.dart

@@ -82,4 +82,9 @@ final class HttpClient {
     return await http.Response.fromStream(streamedResponse)
         .timeout(_httpProperties.readTimeout);
   }
+
+  /// Close the underlying HTTP client and free its resources.
+  void close() {
+    _client.close();
+  }
 }

packages/common_client/lib/src/data_sources/streaming_data_source.dart

@@ -160,6 +160,7 @@ final class StreamingDataSource implements DataSource {
     _stopped = true;
     _pollGeneration++;
     _pollActiveSince = null;
+    _pollingClient.close();
     _dataController.close();
   }