add very basic tests and action

includes action for build. plus tests, fmt and vet

.github/workflows/ci.yml

@@ -0,0 +1,35 @@
+name: CI
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+    branches: [main]
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: actions/setup-go@v5
+        with:
+          go-version-file: go.mod
+          cache: true
+
+      - name: Build
+        run: go build ./...
+
+      - name: Format check
+        run: |
+          if [ -n "$(gofmt -l .)" ]; then
+            echo "The following files are not formatted:"
+            gofmt -l .
+            exit 1
+          fi
+
+      - name: Vet
+        run: go vet ./...
+
+      - name: Test
+        run: go test ./...