[BUG] 具有字段长度定义的 DBML 会引发 SQL 生成错误

Describe the bug Create a generic-type diagram. After importing DBML, if the DBML contains field length specifications, the table column types will be displayed in the format such as VARCHAR(50). When exporting to MySQL, these types are recognized as custom types, causing an export error with an "undefined" prompt. After troubleshooting and fixing the problem, all column types in the exported SQL are unexpectedly converted to JSON.