feat: use black as linter.

.github/workflows/lint.yml

@@ -29,9 +29,9 @@ jobs:
             which python
             pip install pytest torch cloudpickle cryptography
             pip install ray==2.0.0
-            pip install flake8 # For code style checking
+            pip install black
 
     - name: Lint
       run: |
            . py3/bin/activate
-           flake8
+           black --check --diff .

.isort.cfg

@@ -0,0 +1,14 @@
+[settings]
+# This is to make isort compatible with Black. See
+# https://black.readthedocs.io/en/stable/the_black_code_style.html#how-black-wraps-lines.
+line_length=88
+profile=black
+multi_line_output=3
+include_trailing_comma=True
+use_parentheses=True
+float_to_top=True
+filter_files=True
+
+known_local_folder=ray
+known_third_party=grpc
+sections=FUTURE,STDLIB,THIRDPARTY,FIRSTPARTY,LOCALFOLDER