* refactor: distinguish between UniqueIndex and Index
* add test
* add ParseIndex test
* modify unique to constraint
* modify unique to constraint
* fix MigrateColumnUnique
* fix test
* fix unit test
* update test mod
* add MigrateColumnUnique to Migrator interface
* fix format lint
* add comment
* go mod tidy
* revert: revert MigrateColumn
* resolve conflicts
black-06