Extract Git utilities to utils.go

- Add getOriginRemoteURL and getGitConfigValue functions
- Streamline ResolveSignature return type to *SignatureConfig
- Rename hasMetadataChanges to detectMetadataChange
- Add debug logging before return nil statements
- Use gogit GetRemoteURL and GetFirstRemoteURL methods
- Use gitgo ConfigGet method
- Update dependencies (gitgo v0.0.23, gogit v0.0.20)
- Update README documentation

Upgrade GitHub Actions workflow and enhance documentation

- Upgrade actions/checkout from v4 to v6
- Upgrade actions/setup-go from v5 to v6
- Upgrade golangci/golangci-lint-action from v8 to v9
- Upgrade github/codeql-action from v3 to v4
- Add gca signature-change auto-amend feature documentation
- Optimize example code
- Improve README wording between English/Chinese versions
- Add English/Chinese comments to code
- Remove redundant test code in commit_mate_test.go

Enable amend with metadata changes and improve test coverage

- Add hasMetadataChanges function to allow amend when message, author name, or mailbox differs
- Rename useConfigSignInfo to setFromGitConfig with improved semantics
- Replace defer cleanup with t.Cleanup in test files
- Add comprehensive tests with metadata change scenarios
- Add gitgo v0.0.22 integration in test code
- Add English/Chinese comments to example tests
- Improve comments in commitmate and utils packages
- Update go.mod dependencies
- Add Development Notes section to README with package usage rules

增加配置验证功能和改进用户体验

- 添加 ValidateFlags 方法检查配置冲突
- 完善 mailbox/eddress 双字段支持和优先级逻辑
- 增加全面的验证功能测试覆盖
- 改进 README 文档和高级使用示例
- 优化代码注释和文档说明

稍微改改测试和文档-替换崩溃断言为使用三方包-给文档补徽章

增加config-exmaple的子命令让操作更自然些

修改些小问题-在文档里提供更优秀的别名设置样例

简单优化代码

让用户能配置以不同的身份提交代码

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