Add SchedulerMetricsReporter and route metrics state through it (#25629)

test/registered/unit/managers/test_scheduler_chunked_req_gate.py

@@ -77,6 +77,7 @@ def _scheduler_for_get_next_batch(*, tree_cache, chunked_req) -> Scheduler:
     s.dllm_config = None
     s.dllm_manager = None
     s.enable_hisparse = False
+    s.enable_fpm = False
     s.last_batch = None
     s.require_mlp_sync = False
     s.spec_algorithm = MagicMock()