feat: Improve code-style checks and DAG checks (GoogleCloudPlatform#1057)

This change improves the following things:
1. Run pyink in --check mode, since in-place rewrites have no effect on GitHub Actions runners.
2. Run pyink with --diff so contributors can inspect formatting details and make follow-up adjustments.
3. Parallelize DAG checks to reduce overall runtime.

Author: alfredyu-cienet

scripts/code-style.sh

@@ -21,7 +21,7 @@ FOLDERS_TO_FORMAT=("dags" "xlml")
 
 for folder in "${FOLDERS_TO_FORMAT[@]}"
 do
-  pyink "$folder" --pyink-indentation=2 --pyink-use-majority-quotes --line-length=80
+  pyink "$folder" --pyink-indentation=2 --pyink-use-majority-quotes --line-length=80 --check --diff
 done
 
 for folder in "${FOLDERS_TO_FORMAT[@]}"

scripts/dag-check.sh

@@ -14,5 +14,6 @@
 
 export PYTHONPATH=$PWD
 export XLMLTEST_CONFIGS=$PWD/dags/jsonnet/
+export CORES="$(nproc)"
 
-find dags -name '*.py' |  xargs -n 1 -t python
+find dags -name '*.py' -print0 | xargs -0 -n 1 -P "${CORES}" -t python