Bump isort, enable Cython package resorting (#806)

With rapidsai/integration#286, the version of isort running on gpuCI will be bumped to 5.6.4, allowing us to enforce the sorting of packages in Cython (pyx, pxd) files. This PR intends to:

- Enable these checks in the gpuCI style script
- Enable Cython package resorting in the pre-commit hook
- Resort all the Cython files in this repo so they pass the newly enabled checks

Authors:
  - Charles Blackmon-Luca (https://github.com/charlesbluca)

Approvers:
  - Dillon Cullinan (https://github.com/dillon-cullinan)

URL: #806

.pre-commit-config.yaml

@@ -1,8 +1,13 @@
 repos:
-    - repo: https://github.com/timothycrosley/isort
-      rev: 5.0.7
+    - repo: https://github.com/pycqa/isort
+      rev: 5.6.4
       hooks:
           - id: isort
+            args: ["--settings-path=python/setup.cfg"]
+            files: python/.*
+            exclude: __init__.py$
+            types: [text]
+            types_or: [python, cython]
     - repo: https://github.com/ambv/black
       rev: 19.10b0
       hooks:

ci/checks/style.sh

@@ -15,7 +15,7 @@ LANG=C.UTF-8
 conda activate rapids
 
 # Run isort and get results/return code
-ISORT=`isort --recursive --check-only python`
+ISORT=`isort --check-only python --settings-path=python/setup.cfg `
 ISORT_RETVAL=$?
 
 # Run black and get results/return code