Add Codecov integration and badge

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: schigh

.github/workflows/ci.yml

@@ -26,6 +26,10 @@ jobs:
             exit 1
           fi
       - run: go vet ./...
+      - name: Upload coverage reports to Codecov
+        uses: codecov/codecov-action@v5
+        with:
+          token: ${{ secrets.CODECOV_TOKEN }}
 
   bench:
     runs-on: ubuntu-latest

.gitignore

@@ -1 +1,2 @@
 .idea/
+.gstack/

README.md

@@ -1,6 +1,7 @@
 [![CI](https://github.com/schigh/str/actions/workflows/ci.yml/badge.svg)](https://github.com/schigh/str/actions/workflows/ci.yml)
 [![Go Reference](https://pkg.go.dev/badge/github.com/schigh/str.svg)](https://pkg.go.dev/github.com/schigh/str)
 [![Go Report Card](https://goreportcard.com/badge/github.com/schigh/str)](https://goreportcard.com/report/github.com/schigh/str)
+[![codecov](https://codecov.io/github/schigh/str/graph/badge.svg?token=vzYvIwXOLk)](https://codecov.io/github/schigh/str)
 
 # str