fix: support enum columns for mysqlsh copy-instance utility

[fanyang01]

This PR addresses an issue encountered when using MySQL Shell to copy a table containing both a UUID column and an ENUM column:

MySQL Error 1105 (HY000): Conversion Error: Unimplemented type for cast (BIGINT -> ENUM('draft', 'published', 'archived')): LOAD DATA LOCAL INFILE 'memory/testdb@documents@@0.tsv' REPLACE INTO TABLE `testdb`.`documents` CHARACTER SET 'utf8mb4' FIELDS TERMINATED BY '	' ESCAPED BY '\\' LINES STARTING BY '' TERMINATED BY '\n' (@`id`, `title`, `status`, `created_at`) SET `id` = FROM_BASE64(@`id`)

The root cause is that the go-mysql-server framework parses ENUM fields into ordinal values, whereas DuckDB does not support inserting ordinals directly into ENUM columns.

Ref: #329

[Copilot]

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.