fix(config): server_url should return a valid URI for IPv6 hosts

[chen-anders]

Datadog's ddtrace-rb relies on the RedisClient::Config#server_url to return a valid redis:// address as part of initializing its tracing middleware.

https://github.com/DataDog/dd-trace-rb/blob/master/lib/datadog/tracing/contrib/redis/trace_middleware.rb#L79

With an IPv6 redis instance, sidekiq 7.2 would not start up due to bad URI(is not URI?): "redis://fd1b:ac4a:ab80::fcf:6379/12"which URI fails to parse properly.

This PR makes it so we try to detect an IPv6 address in the host and return a valid redis:// address in that particular case.

[byroot]

Thanks for the patch, it looks good, but could you add a regression test?

[chen-anders]

@byroot - just added some more assertions to the server_url tests

[chen-anders]

Can we rerun the Ruby 3.2 suite? Seems like something might've been flakey if tests passed on all other Ruby / redis versions.