gh-89083: add support for UUID version 6 (RFC 9562)

[picnixz]

In light of the discussion in #89083, I decided to remove the previous commits on version 7 and 8 and restrict this specific PR to version 6 only. The previous post can be found in the history of this message.

For version 7, please discuss it on #121119. I won't prepare something for version 8 since the implementation is still not yet decided.

• Issue: Support UUIDv6, UUIDv7, and UUIDv8 from RFC 9562 #89083

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📚 Documentation preview 📚: https://cpython-previews--120650.org.readthedocs.build/

[merwok]

I am puzzled by the PR title change – can you explain?

[picnixz]

Oh yes, after we discussed the v7 implementation, I preferred splitting the PR into 3 with one PR for each version. The ref. impl. means reference implementation but maybe I should have use the expanded wording? (I wanted to have the same title as for the v7 and not a too long title)

[merwok]

«Reference implementation» makes me think that this code is in support or a spec, and maybe not best-written or optimized for production. If this is not the case, just «implementation» or «support» like before has the right connotations 🙂

[picnixz]

Sure, I can make the change if you want (I'll edit the other title as well)