Add CI workflow for automated builds and tests in Github

- Adds a GitHub Actions workflow for linting, testing, and pushing to GHCR.
- Uses uv for environment management and dependency installation.
- Includes Ruff for linting and pytest for testing.
- Uploads test coverage to Codecov.
- Pushes the Docker image to GHCR on pushes to the master branch.

.github/workflows/ci.yml

@@ -0,0 +1,65 @@
+name: CI + Push to GHCR
+
+on:
+  push:
+    branches:
+      - master
+
+jobs:
+  lint:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+
+      - name: Install uv
+        run: |
+          curl -LsSf https://astral.sh/uv/install.sh | sh
+          echo "$HOME/.cargo/bin" >> $GITHUB_PATH
+
+      - name: Lint with Ruff
+        run: |
+          uv venv .venv
+          source .venv/bin/activate
+          uv sync
+          uv run ruff check
+          uv run ruff format --check
+
+  test:
+    runs-on: ubuntu-latest
+    needs: lint
+    steps:
+      - uses: actions/checkout@v3
+
+      - name: Install uv
+        run: |
+          curl -LsSf https://astral.sh/uv/install.sh | sh
+          echo "$HOME/.cargo/bin" >> $GITHUB_PATH
+
+      - name: Run tests
+        run: |
+          uv venv .venv
+          source .venv/bin/activate
+          uv sync
+          uv run pytest -v --cov=. --cov-report=xml
+
+      - name: Upload to Codecov
+        run: bash <(curl -s https://codecov.io/bash)
+
+  push_to_ghcr:
+    runs-on: ubuntu-latest
+    needs: test
+    if: github.ref == 'refs/heads/master'
+    steps:
+      - uses: actions/checkout@v3
+
+      - name: Log in to GHCR
+        run: echo "${{ secrets.REGISTRY_TOKEN }}" | docker login ghcr.io -u ${{ github.actor }} --password-stdin
+
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v2
+
+      - name: Build and push to GHCR
+        run: |
+          docker buildx build --push \
+            --tag ghcr.io/${{ github.repository_owner }}/subscleaner:latest \
+            .