nebula-python客户端查询tag的默认值出错

这个是设计上的问题，服务端 meta 存的默认值，是不能直接解码的。

如果实在需要，可以通过 graph 客户端的 desc tag xxx

(root@nebula) [sf0_1]> desc tag player
+--------+------------+-------+--------------+---------+
| Field  | Type       | Null  | Default      | Comment |
+--------+------------+-------+--------------+---------+
| "name" | "string"   | "YES" | "aaa"        |         |
| "age"  | "int64"    | "YES" | 21           |         |
| "dt"   | "datetime" | "YES" | "datetime()" |         |
| "t"    | "datetime" | "YES" | "datetime()" |         |
+--------+------------+-------+--------------+---------+
Got 4 rows (time spent 469/16595 us)