[Core] put small objects in memory store (#8972)

* remove the put in memory store

* put small objects directly in memory store

* cast data type

* fix another place that uses Put to spill to plasma store

* fix multiple tests related to memory limits

* partially fix test_metrics

* remove not functioning codes

* fix core_worker_test

* refactor put to plasma codes

* add a flag for the new feature

* add flag to more places

* do a warmup round for the plasma store

* lint

* lint again

* fix warmup store

* Update _raylet.pyx

Co-authored-by: Eric Liang <ekhliang@gmail.com>

python/ray/tests/test_multi_node.py

@@ -174,8 +174,10 @@ def test_cleanup_on_driver_exit(call_ray_start):
     driver_script = """
 import time
 import ray
+import numpy as np
 ray.init(address="{}")
-object_ids = [ray.put(i) for i in range(1000)]
+object_ids = [ray.put(np.zeros(200 * 1024, dtype=np.uint8))
+              for i in range(1000)]
 start_time = time.time()
 while time.time() - start_time < 30:
     if len(ray.objects()) == 1000: