HDDS-15895. Make ServerNotLeaderException suggested leader flow IPv6-safe

[chihsuan]

What changes were proposed in this pull request?

ServerNotLeaderException carries the SCM suggested-leader address through its exception message. The IPv6 fast path was broken at three points:

1. The server joined host and port with a plain colon, producing an ambiguous value such as 2001:db8::1:9863.
2. The client-side regex rejected colons in the host, so reconstructing the exception through Hadoop RPC returned no suggested leader.
3. The failover proxy compared formatted address strings. Even after parsing a bracketed IPv6 authority, the comparison could still fail because equivalent IPv6 addresses may use compressed and expanded text forms.

This change fixes the complete flow:

• Build the suggested-leader authority with HddsUtils.getHostPortString, producing [2001:db8::1]:9863 for IPv6 while leaving hostname and IPv4 output unchanged.
• Extend SUGGESTED_LEADER_PATTERN to accept bracketed IPv6 without changing the existing non-IPv6 parsing behavior.
• Parse the suggested leader with NetUtils.createSocketAddr and match it against the configured SCM InetSocketAddress instead of comparing strings.
• Log and ignore an unparseable suggested-leader hint, preserving the existing round-robin fallback rather than interrupting failover.

The result is that IPv6 clients can use the suggested-leader fast path instead of probing SCM nodes in round-robin order.

This issue was found while reviewing HDDS-15773 and kept separate because the message producer, parser, and functional consumer need to change together.

What is the link to the Apache JIRA?

https://issues.apache.org/jira/browse/HDDS-15895

How was this patch tested?

• Added an IPv6 conversion and message round-trip test for ServerNotLeaderException.

• Added a wired three-SCM failover test where the suggested leader is not the next round-robin node. This verifies that the IPv6 hint selects the intended SCM instead of passing accidentally through normal round-robin failover.

• Ran:

  mvn -pl :hdds-common test -Dtest=TestServerNotLeaderExceptionMessageParsing -DskipShade -DskipRecon -DskipDocs
  mvn -pl :hdds-server-framework test -Dtest=TestSCMFailoverProxyProviderRefreshWired -DskipShade -DskipRecon -DskipDocs
  mvn -pl :hdds-common,:hdds-server-framework checkstyle:check -DskipShade -DskipRecon -DskipDocs

Generated-by: Claude Code (Claude Opus 4.8)

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