feat: 新增统一文件模块，统一文件操作

server/pkg/utils/writerx/string_writer.go

@@ -0,0 +1,21 @@
+package writerx
+
+import (
+	"io"
+)
+
+type StringWriter struct {
+	io.WriteCloser
+}
+
+func (sw *StringWriter) WriteString(s string) (n int, err error) {
+	return sw.WriteCloser.Write([]byte(s))
+}
+
+func (sw *StringWriter) Close() error {
+	return sw.WriteCloser.Close()
+}
+
+func NewStringWriter(writer io.WriteCloser) *StringWriter {
+	return &StringWriter{WriteCloser: writer}
+}