The reflectx.Mapper from conn cannot be passed to stmt when creating stmt from conn

[liukaifei]

I set tagMapFunc，but the reflectx.Mapper from conn cannot be passed to stmt when creating stmt from conn. The mapperFor function lacks handling for database connection (conn) types, which prevents the proper propagation of the reflectx.Mapper to statements created from connections.

func setDBTagMapper(db *sqlx.DB, dbtype DBType) {
	switch dbtype {
	case DBTypeDM, DBTypeORA:
		db.Mapper = reflectx.NewMapperTagFunc("db", nil, strings.ToUpper)
	}
}
my func
stmt, err := conn.PreparexContext(ctx, querySql)
if err != nil {
	t.Error(err)
}
defer stmt.Close()

func PreparexContext(ctx context.Context, p PreparerContext, query string) (*Stmt, error) {
	s, err := p.PrepareContext(ctx, query)
	if err != nil {
		return nil, err
	}
	return &Stmt{Stmt: s, unsafe: isUnsafe(p), Mapper: mapperFor(p)}, err
}
func mapperFor(i interface{}) *reflectx.Mapper {
	switch i := i.(type) {
	case DB:
		return i.Mapper
	case *DB:
		return i.Mapper
	case Tx:
		return i.Mapper
	case *Tx:
		return i.Mapper
	default:
		return mapper()
	}
}