ci: add GitHub Actions workflow for fmt, clippy, and tests

.github/workflows/ci.yml

@@ -0,0 +1,43 @@
+name: CI
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+    branches: [main]
+
+env:
+  CARGO_TERM_COLOR: always
+
+jobs:
+  check:
+    name: Check
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+
+      - name: Install Rust toolchain
+        uses: dtolnay/rust-toolchain@master
+        with:
+          toolchain: "1.92"
+          components: rustfmt, clippy
+
+      - name: Cache Cargo artifacts
+        uses: Swatinem/rust-cache@v2
+
+      - name: Download MMDB database
+        run: |
+          mkdir -p data
+          curl -fsSL -o data/Merged-IP.mmdb \
+            "https://github.com/NetworkCats/Merged-IP-Data/releases/latest/download/Merged-IP.mmdb"
+
+      - name: Check formatting
+        run: cargo fmt --check
+
+      - name: Run Clippy
+        run: cargo clippy -- -D warnings
+
+      - name: Run tests
+        run: cargo test