ci: add CI and pin toolchain (#12)

.github/workflows/ci.yml

@@ -0,0 +1,41 @@
+on:
+  pull_request:
+  push:
+    branches:
+      - main
+
+name: CI
+
+jobs:
+  fmt:
+    name: Rustfmt
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v4
+
+      - name: Run cargo fmt
+        env:
+          TERM: xterm-256color
+        run: |
+          cargo fmt --all -- --check
+
+  main:
+    needs: fmt
+    name: ${{ matrix.runs_on }} (clippy, test)
+    runs-on: ${{ matrix.runs_on }}
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - runs_on: macos-latest
+          - runs_on: ubuntu-latest
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v4
+
+      - name: Run cargo clippy
+        run: cargo clippy -- -D warnings
+
+      - name: Run cargo test
+        run: cargo test 

rust-toolchain.toml

@@ -0,0 +1,2 @@
+[toolchain]
+channel = "1.76.0"