[V1][Bugfix] Copy encoder input ids to fix set iteration issue during VLM abort (#13173)

Signed-off-by: andoorve <37849411+andoorve@users.noreply.github.com>

vllm/v1/core/encoder_cache_manager.py

@@ -54,7 +54,7 @@ class EncoderCacheManager:
 
     def free(self, request: Request) -> None:
         """Free all cached input ids for the request."""
-        input_ids = self.get_cached_input_ids(request)
+        input_ids = self.get_cached_input_ids(request).copy()
         for input_id in input_ids:
             self.free_encoder_input(request, input_id)