maint: add code coverage workflow

.github/workflows/coverage.yml

@@ -0,0 +1,33 @@
+# Copyright 2026 Beacon Contributors
+# SPDX-License-Identifier: AGPL-3.0-or-later
+name: Test Coverage
+
+on:
+  push:
+    branches: [ main, dev ]
+  pull_request:
+    branches: [ main ]
+
+jobs:
+  coverage:
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/checkout@v4
+      with:
+        fetch-depth: 2  # Needed for PR diffs
+
+    - name: Set up Go
+      uses: actions/setup-go@v5
+      with:
+        go-version-file: go.mod
+        cache: true
+
+    - name: Install dependencies
+      run: go mod download
+
+    - name: Run tests with coverage
+      run: go test -v -race -coverprofile=coverage.out -covermode=atomic ./...
+
+    - name: Display coverage
+      run: go tool cover -func=coverage.out