ci: add GitHub Actions workflow

Runs on Ubuntu for push-to-master and PRs: installs a Rust toolchain (the
package is a pyo3/maturin extension), uv sync --locked to build it and install
locked deps, then ruff check, ruff format --check, and pytest. Rust and uv
build caches keep it fast.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: ahrzb

.github/workflows/ci.yml

@@ -0,0 +1,43 @@
+name: CI
+
+on:
+  push:
+    branches: [master]
+  pull_request:
+
+concurrency:
+  group: ci-${{ github.ref }}
+  cancel-in-progress: true
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      # The package is a pyo3/maturin extension, so CI needs a Rust toolchain
+      # to build it during `uv sync`.
+      - name: Install Rust toolchain
+        uses: dtolnay/rust-toolchain@stable
+
+      - name: Cache Rust build
+        uses: Swatinem/rust-cache@v2
+
+      - name: Install uv
+        uses: astral-sh/setup-uv@v5
+        with:
+          enable-cache: true
+
+      # Provisions Python 3.14 (per requires-python), builds the extension, and
+      # installs locked deps.
+      - name: Build extension + install deps
+        run: uv sync --locked
+
+      - name: Ruff lint
+        run: uv run ruff check .
+
+      - name: Ruff format
+        run: uv run ruff format --check .
+
+      - name: Tests
+        run: uv run pytest -q