refactor: use dialect-neutral Jet type aliases

Replace mysql/postgres intersection interfaces with mysql type aliases
per go-jet/jet#555 and generalize Apply/Expr signatures.

Co-authored-by: Cursor <cursoragent@cursor.com>

jet_types.go

@@ -1,24 +1,15 @@
 package dbx
 
-import (
-	"github.com/go-jet/jet/v2/mysql"
-	"github.com/go-jet/jet/v2/postgres"
-)
+import "github.com/go-jet/jet/v2/mysql"
 
-// Column is a union type for mysql.Column and postgres.Column
-type Column interface {
-	mysql.Column
-	postgres.Column
-}
+// Column is a dialect-neutral alias for Jet column expressions.
+type Column = mysql.Column
 
-// ColumnList is a union type for mysql.ColumnList and postgres.ColumnList
-type ColumnList interface {
-	mysql.ColumnList
-	postgres.ColumnList
-}
+// ColumnList is a dialect-neutral alias for Jet column lists.
+type ColumnList = mysql.ColumnList
 
-// BoolExpression is a union type for mysql.BoolExpression and postgres.BoolExpression
-type BoolExpression interface {
-	mysql.BoolExpression
-	postgres.BoolExpression
-}
+// Expression is a dialect-neutral alias for Jet SQL expressions.
+type Expression = mysql.Expression
+
+// BoolExpression is a dialect-neutral alias for Jet boolean expressions.
+type BoolExpression = mysql.BoolExpression