Make ZIPCompressedMessage compression level instance-scoped while preserving legacy static API

[Copilot]

ZIPCompressedMessage currently stores compression level in static state, so constructing/configuring one message can unintentionally affect others. This change scopes compression level to each message instance while keeping legacy behavior for older call sites and on-wire compatibility.

• Compression level state model

  • Introduced per-instance compressionLevel.
  • Kept static setLevel(int) as a default-setting API for newly created messages.
  • Constructor overload with explicit level now sets only that instance.

• Backward compatibility

  • Serialization/deserialization format is unchanged (ZIPSerializer behavior unchanged), so peers on older versions can still parse messages.
  • Existing uses of ZIPCompressedMessage.setLevel(...) continue to work as a global default for future instances.

• API/docs cleanup

  • Added setCompressionLevel(int) for explicit instance-level configuration.
  • Updated JavaDoc to reflect default-vs-instance semantics and corrected ZIP level wording (1 = fastest/least compression, 9 = slowest/best compression).

• Focused regression coverage

  • Added tests to verify:
    • instance-specific level does not leak across messages
    • static default still applies only to subsequently created instances

ZIPCompressedMessage.setLevel(6); // default for new instances

ZIPCompressedMessage a = new ZIPCompressedMessage(msgA);      // level 6
ZIPCompressedMessage b = new ZIPCompressedMessage(msgB, 1);   // level 1 (instance-only)
ZIPCompressedMessage c = new ZIPCompressedMessage(msgC);      // still level 6

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• dl.google.com
  • Triggering command: /usr/lib/jvm/temurin-17-jdk-amd64/bin/java /usr/lib/jvm/temurin-17-jdk-amd64/bin/java --add-opens=java.base/java.lang=ALL-UNNAMED --add-opens=java.base/java.lang.invoke=ALL-UNNAMED --add-opens=java.base/java.util=ALL-UNNAMED --add-opens=java.prefs/java.util.prefs=ALL-UNNAMED --add-exports=jdk.compiler/com.sun.tools.javac.api=ALL-UNNAMED --add-exports=jdk.compiler/com.sun.tools.javac.util=ALL-UNNAMED --add-opens=java.base/java.util=ALL-UNNAMED --add-opens=java.prefs/java.util.prefs=ALL-UNNAMED --add-opens=java.base/java.nio.charset=ALL-UNNAMED --add-opens=java.base/java.net=ALL-UNNAMED --add-opens=java.base/java.util.concurrent=ALL-UNNAMED --add-opens=java.base/java.util.concurrent.atomic=ALL-UNNAMED --add-opens=java.xml/javax.xml.namespace=ALL-UNNAMED --add-opens=java.base/java.time=ALL-UNNAMED -XX:MaxMetaspaceSize=384m -XX:+HeapDumpOnOutOfMemoryError -Xms256m -Xmx512m -Dfile.encoding=UTF-8 (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)