added unsigned big integers support for mysql

[serejkaaa512]

Fixes this.

[serejkaaa512]

@janpio Can you take a look, please?

[janpio]

Took a look, but I know neither Rust nor the quaint codebase and my MySQL knowledge is also frozen on a 3.x version 🤣 A maintainer of this repository will take a look earlier or later though, don't worry.

[pimeys]

This needs somebody from the client team to take a look, it might need some changes in the query engine. Already talked with @dpetrick a few days back, so it is part of their schedule.