Code coverage (#5)

* Add code coverage workflow

* Add code coverage badge

Author: MDobak

.github/workflows/coverage.yaml

@@ -0,0 +1,37 @@
+name: coverage
+on:
+  push:
+    tags:
+      - v*
+    branches:
+      - main
+  pull_request:
+
+jobs:
+  coverage:
+    name: Report Coverage
+    runs-on: ubuntu-latest
+    steps:
+      - name: Install Go
+        uses: actions/setup-go@v4
+        with:
+          go-version: "1.24.x"
+
+      - name: Check out code
+        uses: actions/checkout@v4
+
+      - name: Install deps
+        run: |
+          go mod download
+
+      - name: Run tests with coverage output
+        run: |
+          go test -race -covermode atomic -coverprofile=covprofile ./...
+
+      - name: Install goveralls
+        run: go install github.com/mattn/goveralls@latest
+
+      - name: Send coverage
+        env:
+          COVERALLS_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+        run: goveralls -coverprofile=covprofile -service=github

README.md

@@ -1,6 +1,6 @@
 # go-xerrors
 
-[![Go Reference](https://pkg.go.dev/badge/github.com/mdobak/go-xerrors.svg)](https://pkg.go.dev/github.com/mdobak/go-xerrors) [![Go Report Card](https://goreportcard.com/badge/github.com/mdobak/go-xerrors)](https://goreportcard.com/report/github.com/mdobak/go-xerrors) [![License: MIT](https://img.shields.io/badge/License-MIT-yellow.svg)](https://opensource.org/licenses/MIT)
+[![Go Reference](https://pkg.go.dev/badge/github.com/mdobak/go-xerrors.svg)](https://pkg.go.dev/github.com/mdobak/go-xerrors) [![Go Report Card](https://goreportcard.com/badge/github.com/mdobak/go-xerrors)](https://goreportcard.com/report/github.com/mdobak/go-xerrors) [![License: MIT](https://img.shields.io/badge/License-MIT-yellow.svg)](https://opensource.org/licenses/MIT) [![Coverage Status](https://coveralls.io/repos/github/MDobak/go-xerrors/badge.svg?branch=coverage)](https://coveralls.io/github/MDobak/go-xerrors?branch=coverage)
 
 `go-xerrors` is a simple, idiomatic, lightweight Go package that provides utilities for error handling. It offers functions and types to support stack traces, multi-errors, and simplified panic handling. The package is compatible with Go's standard error handling mechanisms, such as `errors.As`, `errors.Is`, and `errors.Unwrap`, including features from Go 1.13 and 1.20.