(core) Python optimizations to speed up data engine

Summary:
- A bunch of optimizations guided by python profiling (esp. py-spy)
- Big one is optimizing Record/RecordSet attribute access
- Adds tracemalloc printout when running test_replay with PYTHONTRACEMALLOC=1 (on PY3)
  (but memory size is barely affected by these changes)

- Testing with RECORD_SANDBOX_BUFFERS_DIR, loading and calculating a particular
  very large doc (CRM), time taken improved from 73.9s to 54.8s (26% faster)

Test Plan: No behavior changes intended; relying on existing tests to verify that.

Reviewers: georgegevoian

Reviewed By: georgegevoian

Differential Revision: https://phab.getgrist.com/D3781

sandbox/grist/test_replay.py

@@ -44,7 +44,7 @@ import unittest
 
 from main import run
 from sandbox import Sandbox
-
+import six
 
 def marshal_load_all(path):
   result = []
@@ -65,6 +65,7 @@ class TestReplay(unittest.TestCase):
     root = os.environ.get("RECORD_SANDBOX_BUFFERS_DIR")
     if not root:
       self.skipTest("RECORD_SANDBOX_BUFFERS_DIR not set")
+
     for dirpath, dirnames, filenames in os.walk(root):
       if "input" not in filenames:
         continue
@@ -76,9 +77,18 @@ class TestReplay(unittest.TestCase):
       new_output_path = os.path.join(dirpath, "new_output")
       with open(input_path, "rb") as external_input:
         with open(new_output_path, "wb") as external_output:
+          if six.PY3:
+            import tracemalloc          # pylint: disable=import-error
+            tracemalloc.reset_peak()
+
           sandbox = Sandbox(external_input, external_output)
           run(sandbox)
 
+          # Run with env PYTHONTRACEMALLOC=1 to trace and print peak memory (runs much slower).
+          if six.PY3 and tracemalloc.is_tracing():
+            mem_size, mem_peak = tracemalloc.get_traced_memory()
+            print("mem_size {}, mem_peak {}".format(mem_size, mem_peak))
+
       original_output = marshal_load_all(output_path)
 
       # _send_to_js does two layers of marshalling,