feat : add radix prefix cache

- replace hash-only lookup with page-granular radix matching
- keep partial pages private and cache only materialized KV prefixes
- integrate completed-request caching and add radix behavior tests

astrai/inference/__init__.py

@@ -35,7 +35,7 @@ from astrai.inference.core import (
     KVCache,
     KVStorage,
     PagePool,
-    PrefixCache,
+    RadixCache,
     ReqToTokenPool,
     Task,
     TaskManager,
@@ -66,7 +66,7 @@ __all__ = [
     "KVCache",
     "KVStorage",
     "PagePool",
-    "PrefixCache",
+    "RadixCache",
     "ReqToTokenPool",
     "page_hash",
     "sample",