Refactor prefix cache type checking (#17028)

python/sglang/srt/mem_cache/chunk_cache.py

@@ -30,6 +30,9 @@ class ChunkCache(BasePrefixCache):
 
         self.protected_size_ = 0
 
+    def is_chunk_cache(self) -> bool:
+        return True
+
     # NOTE (csy): this is to determine if a cache has prefix matching feature.
     # Chunk cache always return True to indicate no prefix matching.
     # TODO (csy): Using a prefix cache trait to replace this
@@ -106,6 +109,9 @@ class SWAChunkCache(ChunkCache):
 
         self.chunked_prefill_size = params.chunked_prefill_size
 
+    def supports_swa(self) -> bool:
+        return True
+
     def evict_swa(
         self,
         req: Req,