[minor] Perf optimizations for direct actor task submission (#6044)

* merge optimizations

* fix

* fix memory err

* optimize

* fix tests

* fix serialization of method handles

* document weakref

* fix check

* bazel format

* disable on 2

python/ray/ray_perf.py

@@ -10,19 +10,19 @@ import ray
 filter_pattern = os.environ.get("TESTS_TO_RUN", "")
 
 
-@ray.remote
+@ray.remote(num_cpus=0)
 class Actor(object):
     def small_value(self):
-        return 0
+        return b"ok"
 
     def small_value_arg(self, x):
-        return 0
+        return b"ok"
 
     def small_value_batch(self, n):
         ray.get([small_value.remote() for _ in range(n)])
 
 
-@ray.remote
+@ray.remote(num_cpus=0)
 class Client(object):
     def __init__(self, servers):
         if not isinstance(servers, list):
@@ -45,7 +45,7 @@ class Client(object):
 
 @ray.remote
 def small_value():
-    return 0
+    return b"ok"
 
 
 @ray.remote