WIP: Select() using iterator

[YuriyNasretdinov]

Hi, given the recent proposal for generic methods being accepted into Go (golang/go#77273) I'd like to propose an interator API for Select() which looks like this:

for u, err := db.SelectIter[User]("SELECT * FROM users") {
    if err != nil { ... }
    ...
}

This API allows to have convenience of Select() without having to pre-allocate the entire result. The use-case is kinda niche, but without generic methods all other options look much uglier (example: https://github.com/YuriyNasretdinov/sqly).

The code works, however I'm happy to hear your feedback. Marked as WIP since I'd like to add more tests and, crucially, Go 1.27 isn't out yet. The tests do pass on gotip though, no GOEXPERIMENT needed