发送rpc请求代码：https://github.com/tikv/client-go/blob/dc130aa0d3b1cdd4eeb8b26caa3299d4fafb4a30/internal/client/client.go#L535
对请求参数编码代码：https://github.com/tikv/client-go/blob/dc130aa0d3b1cdd4eeb8b26caa3299d4fafb4a30/internal/client/api_version.go#L126