ci: add GitHub Actions test workflow

Add automated testing workflow that runs on push and pull requests
to main branch. Includes Go module caching and code coverage
reporting via Codecov.

Author: hrntknr

.github/workflows/test.yaml

@@ -0,0 +1,42 @@
+name: Test
+
+on:
+  push:
+    branches:
+      - main
+  pull_request:
+    branches:
+      - main
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+
+      - name: Set up Go
+        uses: actions/setup-go@v4
+        with:
+          go-version: "1.23"
+
+      - name: Cache Go modules
+        uses: actions/cache@v3
+        with:
+          path: ~/go/pkg/mod
+          key: ${{ runner.os }}-go-${{ hashFiles('**/go.sum') }}
+          restore-keys: |
+            ${{ runner.os }}-go-
+
+      - name: Download dependencies
+        run: go mod download
+
+      - name: Run tests
+        run: go test -v ./...
+
+      - name: Run tests with coverage
+        run: go test -v -coverprofile=coverage.out ./...
+
+      - name: Upload coverage to Codecov
+        uses: codecov/codecov-action@v3