Refactor BUILD file to create container_service library

Also fix resulting pytype errors that this exposed.

PiperOrigin-RevId: 846252648

Author: p3rf Team

perfkitbenchmarker/container_service/base.py

@@ -17,7 +17,7 @@
 import itertools
 import os
 import time
-from typing import Any, Iterable
+from typing import Any, Callable, Iterable
 
 from absl import flags
 from perfkitbenchmarker import context
@@ -583,7 +583,7 @@ def GetNodePoolNames(self) -> list[str]:
 
 def GetContainerClusterClass(
     cloud: str, cluster_type: str
-) -> type[BaseContainerCluster]:
+) -> Callable[[container_spec_lib.ContainerClusterSpec], BaseContainerCluster]:
   return resource.GetResourceClass(
       BaseContainerCluster, CLOUD=cloud, CLUSTER_TYPE=cluster_type
   )

perfkitbenchmarker/linux_benchmarks/kubernetes_ai_inference_benchmark.py

@@ -118,7 +118,9 @@ def Run(
   cluster: container_service.KubernetesCluster = (
       benchmark_spec.container_cluster
   )
-  server: k8s_server.WGServingInferenceServer = cluster.inference_server
+  server: kubernetes_inference_server.BaseKubernetesInferenceServer | None = (
+      cluster.inference_server
+  )
   if not server or not isinstance(server, k8s_server.WGServingInferenceServer):
     raise ValueError('Inference server is not initialized in the cluster.')