Support Go 1.23 iterator

[FlowingSPDG]

Hi, thank you for maintaining nice project!

Some Go 1.23 adds official iterator(iter.Seq), I think this package can also support itas well.

I'll make a PR once I got time to work on this.

[klauspost]

No problem. Simple rules:

A) No API breaking.
B) Guard behind go1.23 build tags, so Go 1.21 and 1.22 will work.
C) Reasonable documentation and tests (ie "none" will not be accepted)