https://github.com/uuid6/uuid6-ietf-draft/

A simple test case to show that these are actually sortable variants:
```
uuid6_1 = uuid6()
uuid7_1 = uuid7()
for _ in range(100000):
    uuid6_2 = uuid6()
    uuid7_2 = uuid7()
    assert uuid6_1 < uuid6_2
    assert uuid7_1 < uuid7_2
    uuid6_1, uuid7_1 = uuid6_2, uuid7_2

print(uuid6_1)
print(uuid7_1)
```