[HiCache] fix compatibility bugs with eagle and HiCacheStorage (#19570)

Co-authored-by: maoyuhan <susanmao1997@outlook.com>

python/sglang/srt/mem_cache/hiradix_cache.py

@@ -39,6 +39,7 @@ from sglang.srt.mem_cache.radix_cache import (
     compute_node_hash_values,
     split_node_hash_value,
 )
+from sglang.srt.mem_cache.utils import convert_to_bigram_key
 from sglang.srt.observability.metrics_collector import StorageMetricsCollector
 from sglang.srt.utils import bind_to_closest_numa_node_cuda
 
@@ -1298,6 +1299,11 @@ class HiRadixCache(RadixCache):
         last_hash: Optional[str] = None,
         prefix_keys: Optional[List[str]] = None,
     ):
+        new_input_tokens = (
+            convert_to_bigram_key(new_input_tokens)
+            if self.is_eagle
+            else new_input_tokens
+        )
         # align the number of fetching tokens to the page size
         prefetch_length = len(new_input_tokens) - (
             len(new_input_tokens) % self.page_size