fix the type of ResultSetHeader **insertId** attribute type

[buuug7]

database table ID either number or string

[testn]

Nope. LastInsertId has to be number.

https://dev.mysql.com/doc/internals/en/packet-OK_Packet.html

[sidorares]

when bigNumberStrings setting is set to true insertId is returned as string ( when it can't fit js number )

[testn]

ah I forgot

[sidorares]

I'm not a fan of this polymorphic results but not quite sure how to improve ( and in backwards compatible way )

we can probably retire Long.js and return native BigInt here so the type will be number | BigInt ( still polymorphic )