[NET-741] Add subnet IPv6 handling

[see-quick]

This PR adds SubnetUtils6 to also support IPv6 CIDR notation, as the end user could possibly need handling not just the IPv4 stack. Moreover, I have added tests to cover this functionality accordingly.

[see-quick]

Since there hasn't been much feedback so far... I want to ask whether this approach is okay or if you prefer a different direction?

cc @garydgregory or other maintainers @sebbASF ?

[isaric]

Hey @see-quick , is there a JIRA issue for this PR?
If yes, please include the tag in the title of the PR. You should also include the tag in the commits.
If there is no issue, you should write one and get the issue reviewed. After that, you can include the tag here and the PR can be reviewed.

[garydgregory]

Since there hasn't been much feedback so far... I want to ask whether this approach is okay or if you prefer a different direction?

cc @garydgregory or other maintainers @sebbASF ?

I'll try take a look this week...

[see-quick]

Hi, I have opened the KIP-1276 , which is currently under discussion. This change helps enable the functionality described in the KIP. I appreciate your time and feedback.

[garydgregory]

The Jira ticket is https://issues.apache.org/jira/browse/NET-741

[garydgregory]

Hello @see-quick

I'm sorry I haven't commented here for a while.

I think it would be nice to have a test class or method that specifically tests all the examples in https://datatracker.ietf.org/doc/html/rfc5952

The Javadoc should also point to the RFC.

[garydgregory]

Add a Javadoc to describe the format. Is there an expectation that this string can be fed back in the constructor? Either way, testToString should test that use case.