[Feature] Add process-local in-memory KV indexer and Router integration (#33370)

Co-authored-by: Wu, Yutong <yutong.wu@amd.com>
Co-authored-by: TianDi101 <ditian12@amd.com>
Co-authored-by: Zhangheng <hzh0425@apache.org>

experimental/sgl-router/sgl-kv-indexer/tests/common/id.rs

@@ -0,0 +1,11 @@
+// SPDX-FileCopyrightText: Copyright (c) 2026 The SGLang Authors
+// SPDX-License-Identifier: Apache-2.0
+
+use std::time::{SystemTime, UNIX_EPOCH};
+
+pub fn nanos() -> u128 {
+    SystemTime::now()
+        .duration_since(UNIX_EPOCH)
+        .unwrap()
+        .as_nanos()
+}