Test MariaDB & MySQL handling of decimal type with negative scale

[findepi]

The connectors claim support for decimal with negative scale

trino/plugin/trino-mariadb/src/main/java/io/trino/plugin/mariadb/MariaDbClient.java

Line 393 in 89dc934

precision = precision + max(-decimalDigits, 0); // Map decimal(p, -s) (negative scale) to decimal(p+s, 0).

trino/plugin/trino-mysql/src/main/java/io/trino/plugin/mysql/MySqlClient.java

Lines 602 to 603 in 489f053

	// TODO does mysql support negative scale?
	precision = precision + max(-decimalDigits, 0); // Map decimal(p, -s) (negative scale) to decimal(p+s, 0).

it's not tested and may not work

• see Trino fails when PostgreSQL table has a decimal/numeric column with negative scale #28388
• see Fix PostgreSQL connector handling of extreme decimal scales #28414

[sunghj1118]

Hi @findepi, I'm a first-time contributor to Trino and would love to work on this! I'm already familiar with MySQL/MariaDB and can start on the test cases immediately. Could you please assign this to me?