Replace sortslice with sortx and fix bug in HasLetterPrefix function

- Fix HasLetterPrefix used len(runes) instead of runes[0]
- Add bounds checks when strings are blank in HasLetterPrefix and CapitalizeFirst
- Replace sortslice with sortx in goi18n.go
- Add English/Chinese comments to each utils function
- Optimize inline comment style in goi18n.go
- Update dependencies in go.mod and go.sum
- Update GitHub Actions workflow and Makefile
- Update README.zh.md
- Add comprehensive test cases increasing utils coverage from 17.4% to 100%

经过学习发现并不需要在写文件时手动保持权限

简单优化代码增加配置项

探索使用中文做键的可行性

补充测试和修改文档

把复杂的示例结构改简单

适配复数形式

补充测试内容

实现基本功能