Add GitHub Actions workflow for PyPI publishing

.github/workflows/publish.yml

@@ -0,0 +1,51 @@
+name: CI + Publish to PyPI
+
+on:
+  push:
+    branches:
+      - main
+    tags:
+      - "v*"
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout repo
+        uses: actions/checkout@v4
+
+      - name: Set up Python
+        uses: actions/setup-python@v5
+        with:
+          python-version: "3.12"
+
+      - name: Install build backend
+        run: pip install build
+
+      - name: Build package
+        run: python -m build
+
+      - name: Upload build artifact
+        uses: actions/upload-artifact@v4
+        with:
+          name: dist-files
+          path: dist/
+
+  publish:
+    needs: build
+    runs-on: ubuntu-latest
+    if: startsWith(github.ref, 'refs/tags/v')
+
+    steps:
+      - name: Download build artifacts
+        uses: actions/download-artifact@v4
+        with:
+          name: dist-files
+          path: dist/
+
+      - name: Publish to PyPI
+        uses: pypa/gh-action-pypi-publish@release/v1
+        with:
+          password: ${{ secrets.PYPI_API_TOKEN }}
+          skip_existing: true