[Router] Add bucket-aware policy domains and native cache indexing (#38108)

Signed-off-by: Vincent Gao <vincentbo@linux.alibaba.com>
Co-authored-by: inkcherry <mingzhi.liu@amd.com>
Co-authored-by: yangbodong22011 <13137470+yangbodong22011@users.noreply.github.com>

experimental/sgl-router/tests/proxy/failover.rs

@@ -35,6 +35,8 @@ async fn failover_when_one_worker_dies() {
             id: "tiny".into(),
             tokenizer_path: "tests/fixtures/tiny_tokenizer.json".into(),
             policy: PolicyKind::RoundRobin,
+            decode_policy: Default::default(),
+            bucket_config: None,
             circuit_breaker: Some(CircuitBreakerConfig {
                 threshold: std::num::NonZeroU32::new(1).unwrap(), // open after first failure
                 cool_down_secs: 30,