RFC9562 was released almost two weeks ago, so we can replace the "draft"
UUIDv7 URL with the final RFC URL too.  RFC9562 obsoletes RFC4122, so I
replaced its link as well.

https://github.com/ruby/securerandom/commit/1e41c3d2cb

We use the following site for that now:

* https://tools.ietf.org/ or http
* https://datatracker.ietf.org or http

Today, IETF said the official site of RFC is www.rfc-editor.org.

FYI: https://authors.ietf.org/en/references-in-rfcxml

I replaced them to www.rfc-editor.org.

https://github.com/ruby/securerandom/commit/b587b8c7cb

https://github.com/ruby/securerandom/commit/e8be08901a

https://github.com/ruby/securerandom/commit/9a99978135

https://github.com/ruby/securerandom/pull/19/files#r1329476195

https://github.com/ruby/securerandom/commit/156cbb8448

Although the specification for UUIDv7 is still in draft, the UUIDv7
algorithm has been relatively stable as it progresses to completion.

Version 7 UUIDs can be very useful, because they are lexographically
sortable, which can improve e.g: database index locality.  See section
6.10 of the draft specification for further explanation:

  https://datatracker.ietf.org/doc/draft-ietf-uuidrev-rfc4122bis/

The specification allows up to 12 bits of extra timestamp precision, to
make UUID generation closer to monotonically increasing.  This provides
between 1ms and ~240ns of timestamp precision.  At the cost of some code
complexity and a small performance penalty, a kwarg may specify any
arbitrary precision between 0 and 12 extra bits.  Any stronger
guarantees of monotonicity have considerably larger tradeoffs, so
nothing more is implemented.  This limitation is documented.

Ruby issue: https://bugs.ruby-lang.org/issues/19735

https://github.com/ruby/securerandom/commit/34ed1a2ec3