GO将mysql 中 decimal 数据类型映射到 protobuf的操作方法

`discount` decimal(10,2) NOT NULL DEFAULT '0.00' COMMENT '折扣',

message Price {
  double discount = 1; // 折扣
}

type Price struct {
	state         protoimpl.MessageState
	sizeCache     protoimpl.SizeCache
	unknownFields protoimpl.UnknownFields

	Discount  float64 `protobuf:"fixed64,6,opt,name=discount,proto3" JSON:"discount"`         // 折扣
}

message Price {
  float discount = 1; // 折扣
}

type Price struct {
	state         protoimpl.MessageState
	sizeCache     protoimpl.SizeCache
	unknownFields protoimpl.UnknownFields

	Discount  float32 `protobuf:"fixed32,1,opt,name=discount,proto3" json:"discount"`         // 折扣
}

goctl model mysql datasource -url="root:123@tcp(127.0.0.1:3306)/数据库名" -table="xxx" -dir=./internal/model