fix(stringer): update error String() impl to remove manual decrement and align with new index logic

update tools: bump stringer to v0.42.0

Author: iseki0

.github/workflows/test.yml

@@ -55,7 +55,7 @@ jobs:
       - name: Install Go tools
         run: |
           cd /tmp
-          go install golang.org/x/tools/cmd/stringer@v0.23.0
+          go install golang.org/x/tools/cmd/stringer@v0.42.0
 
       - name: Go mod tidy
         run: go mod tidy