chore: add CI

.github/workflows/ci.yml

@@ -0,0 +1,41 @@
+# This workflow uses actions that are not certified by GitHub.
+# They are provided by a third-party and are governed by
+# separate terms of service, privacy policy, and support
+# documentation.
+
+name: Test
+
+on:
+  push:
+    branches: ["main"]
+  pull_request:
+
+permissions:
+  contents: read
+
+jobs:
+  build:
+    name: Build and test
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Set up Elixir
+        uses: erlef/setup-beam@v1
+        with:
+          elixir-version: "1.18.3"
+          otp-version: "27"
+      - name: Restore dependencies cache
+        uses: actions/cache@v3
+        with:
+          path: deps
+          key: ${{ runner.os }}-mix-${{ hashFiles('**/mix.lock') }}
+          restore-keys: ${{ runner.os }}-mix-
+      - name: Install dependencies
+        run: mix deps.get
+      - name: Run tests
+        run: mix test
+      - name: Format
+        run: mix format --check-formatted