[Java] Cover IPv6 and dual-stack DNS entrypoint behavior

[dkropachev]

Verify and cover DRIVER-823 behavior in scylladb/alternator-client-java, including IPv6 literals, A-only/AAAA-only DNS, cross-family fallback, recovery, and request routing.

Jira: DRIVER-917
Parent Jira issue: DRIVER-823
Implementation PR: #154

[dkropachev]

Resolved by merged PR #154.