insert method
Implementation
@override
Future<int> insert(String table, Map<String, dynamic> values) async {
final keys = values.keys.join(', ');
final placeholders = List.filled(values.length, '?').join(', ');
final sql = 'INSERT INTO $table ($keys) VALUES ($placeholders)';
db.execute(sql, values.values.toList());
return db.lastInsertRowId;
}