Model MySQL CREATE EVENT and ALTER EVENT

[minleejae]

Summary

• parse MySQL CREATE EVENT and ALTER EVENT as dedicated statements
• expose one-time and recurring schedules, bounds, completion policy, status, comments, rename targets, and bodies as structured AST values
• route event bodies through visitors so contained table references and validation remain usable

Validation

• ./gradlew spotlessApply test spotlessCheck checkstyleMain checkstyleTest
• executed create, reschedule, body replacement, disable, and rename flows against MySQL 8.4