With this change, `Uuid::uuid1()`, `Uuid::uuid2()` and so forth now produce a `LazyUuidFromString` instance, which
is both more memory efficient and comparable to `Uuid::fromString()` instances in other tools, such as within
PHPUnit's `Assertion::assertEqual()`, which would reject any two objects not matching each other's types.
Before this patch, `Assertion::assertEquals(Uuid::uuid5(...), Uuid::fromString(...))` would always fail due to
different subtypes produced by the two factory methods.
Ben Ramsey
Marco Pivetta