Better type casting of BIT values

see similar discussion in https://github.com/sidorares/node-mysql2/issues/1597

Currently BIT fields are always returned as single byte Buffer:

https://github.com/mysqljs/mysql/blob/dc9c152a87ec51a1f647447268917243d2eab1fd/lib/protocol/packets/RowDataPacket.js#L107

I think this should be returned as a number. Might be good to coordinate both changes here in mysql2, this is potentially a breaking backwards incompatible change