ci: add GitHub Actions CI workflow (#6)

* ci: add GitHub Actions workflow with Go 1.25/1.26 matrix

* Update CI workflow to use Go 1.26 only

Removed Go version 1.25 from CI matrix.

.github/workflows/ci.yml

@@ -0,0 +1,30 @@
+name: CI
+
+on:
+  push:
+    branches: [master]
+  pull_request:
+    branches: [master]
+
+permissions:
+  contents: read
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        go-version: ['1.26']
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-go@v5
+        with:
+          go-version: ${{ matrix.go-version }}
+      - run: go vet ./...
+      - run: go test -race -coverprofile=coverage.txt ./...
+      - name: Upload coverage
+        if: matrix.go-version == '1.26'
+        uses: codecov/codecov-action@v4
+        with:
+          files: coverage.txt
+        continue-on-error: true