feat(stringx): 自 go-hua/common 迁入字符串/切片/拼音工具并独立成包

- common 的 string.go/array.go/pinyin.go 拆为 stringx 包（含随机串、GUID、
  通配符匹配、校验规则、链式缓冲、驼峰转下划线、切片删元素、拼音首字母）
- 附单元测试与 examples/stringx 可运行例程、包 README
- go.mod 新增直接依赖 mozillazg/go-pinyin（go-hua 同版本锁 v0.20.0→实际解析 v0.21.0）

go.sum

@@ -63,6 +63,8 @@ github.com/modern-go/concurrent v0.0.0-20180306012644-bacd9c7ef1dd h1:TRLaZ9cD/w
 github.com/modern-go/concurrent v0.0.0-20180306012644-bacd9c7ef1dd/go.mod h1:6dJC0mAP4ikYIbvyc7fijjWJddQyLn8Ig3JB5CqoB9Q=
 github.com/modern-go/reflect2 v1.0.2 h1:xBagoLtFs94CBntxluKeaWgTMpvLxC4ur3nMaC9Gz0M=
 github.com/modern-go/reflect2 v1.0.2/go.mod h1:yWuevngMOJpCy52FWWMvUC8ws7m/LJsjYzDa0/r8luk=
+github.com/mozillazg/go-pinyin v0.21.0 h1:Wo8/NT45z7P3er/9YSLHA3/kjZzbLz5hR7i+jGeIGao=
+github.com/mozillazg/go-pinyin v0.21.0/go.mod h1:iR4EnMMRXkfpFVV5FMi4FNB6wGq9NV6uDWbUuPhP4Yc=
 github.com/pelletier/go-toml/v2 v2.2.4 h1:mye9XuhQ6gvn5h28+VilKrrPoQVanw5PMw/TB0t5Ec4=
 github.com/pelletier/go-toml/v2 v2.2.4/go.mod h1:2gIqNv+qfxSVS7cM2xJQKtLSTLUE9V8t9Stt+h56mCY=
 github.com/pkg/errors v0.9.1 h1:FEBLx1zS214owpjy7qsBeixbURkuhQAwrK5UwLGTwt4=