Missing `#uuid_v4` and `#uuid_v7` methods

#36 added back #alphanumeric keyword arg for characters. But #uuid_v7 (and the #uuid_v4 alias) are still missing:

With ruby 3.2.6 and securerandom 0.3.2:

$ rbenv shell 3.2.6
$ gem install securerandom -v0.3.2
Fetching securerandom-0.3.2.gem
Successfully installed securerandom-0.3.2
Parsing documentation for securerandom-0.3.2
Installing ri documentation for securerandom-0.3.2
Done installing documentation for securerandom after 0 seconds
1 gem installed
$ ruby -rsecurerandom -e "puts SecureRandom.uuid_v7; puts SecureRandom.uuid_v4"
0193e518-54a6-7e66-ab61-99adfce68788
fb00fada-2414-4f60-8c54-97d30f22f536

With ruby 3.2.6 and securerandom 0.4.1:

$ rbenv shell 3.2.6
$ gem install securerandom -v0.4.1
Fetching securerandom-0.4.1.gem
Successfully installed securerandom-0.4.1
Parsing documentation for securerandom-0.4.1
Installing ri documentation for securerandom-0.4.1
Done installing documentation for securerandom after 0 seconds
1 gem installed
$ ruby -rsecurerandom -e "puts SecureRandom.uuid_v7"
-e:1:in `<main>': undefined method `uuid_v7' for SecureRandom:Module (NoMethodError)

puts SecureRandom.uuid_v7
                 ^^^^^^^^
Did you mean?  uuid
$ ruby -rsecurerandom -e "puts SecureRandom.uuid_v4"
-e:1:in `<main>': undefined method `uuid_v4' for SecureRandom:Module (NoMethodError)

puts SecureRandom.uuid_v4
                 ^^^^^^^^
Did you mean?  uuid

Start by reading the SecureRandom API around the existing uuid method and compare the behavior shown for versions 0.3.2 and 0.4.1. Verify that SecureRandom.uuid_v7 and its uuid_v4 alias are available in 0.4.1 and produce UUID values like the examples; add focused coverage for both methods.