refactor: parse localnodes responses with streaming parser

[dkropachev]

Summary

• move /localnodes response parsing out of AlternatorLiveNodes into LocalNodesResponseParser
• replace comma splitting with a streaming JSON string-array parser
• handle empty arrays, malformed bodies, escaped host strings, invalid host entries, and valid multi-host responses
• keep malformed successful /localnodes responses non-fatal on main

Closes #142

Testing

• JAVA_HOME=/usr/lib/jvm/java-11-openjdk-amd64 PATH=/usr/lib/jvm/java-11-openjdk-amd64/bin:$PATH mvn -q -Dtest=LocalNodesResponseParserTest,AlternatorLiveNodesClusterDiscoveryTest,ConnectionLeakTest test
• JAVA_HOME=/usr/lib/jvm/java-11-openjdk-amd64 PATH=/usr/lib/jvm/java-11-openjdk-amd64/bin:$PATH mvn -q fmt:check checkstyle:check