Add linter; fix pipeline

.github/workflows/lint.yml

@@ -0,0 +1,29 @@
+name: Lint
+
+on: [push, pull_request]
+
+jobs:
+  ruff:
+    runs-on: ubuntu-latest
+    steps:
+    - name: Checkout
+      uses: actions/checkout@v4
+    - name: Install ruff
+      run: pip install ruff
+    - name: Check style
+      run: ruff check --config .ruff.toml pyscf
+    - name: Check NumPy
+      run: ruff check --select NPY --ignore NPY002 pyscf
+  flake:
+    runs-on: ubuntu-latest
+    steps:
+    - name: Checkout
+      uses: actions/checkout@v4
+    - name: Set up Python
+      uses: actions/setup-python@v4
+      with:
+        python-version: 3.10
+    - name: Install flake8
+      run: pip install "flake8>=3.7.0"
+    - name: Static analysis
+      run: flake8 --config .flake8 pyscf

.github/workflows/unittest.yml

@@ -12,7 +12,7 @@ jobs:
     - name: Set up Python 3.10
       uses: actions/setup-python@v4
       with:
-        python-version: 3.10
+        python-version: "3.10"
     - name: Install
       run: pip install pyscf packaging pytest
     - name: Test