Exclude cmd/ and examples/ from test coverage calculation

Coverage should only measure library code (pkg/ and root), not command-line
tools and example programs. This brings coverage back to ~96% for the library.

Author: leifj

.github/workflows/ci.yml

@@ -33,7 +33,7 @@ jobs:
       run: go mod verify
 
     - name: Run tests
-      run: go test -v -race -coverprofile=coverage.out ./...
+      run: go test -v -race -coverprofile=coverage.out $(go list ./... | grep -v '/cmd/' | grep -v '/examples/')
 
     - name: Check coverage
       run: |