Replace loop-based string concatenation with StringBuilder in path/polytree string rendering

[Copilot]

This change removes repeated String concatenation inside hot toString loops in core path and polytree types. The goal is to keep output identical while avoiding quadratic string-building behavior.

• Core path string rendering

  • Updated toString() implementations in:
    • Path64
    • PathD
    • Paths64
    • PathsD
  • Replaced s = s + ... loop concatenation with StringBuilder.append(...).

• Polytree string rendering

  • Updated PolyPathBase.toStringInternal(int idx, int level) and PolyPathBase.toString().
  • Replaced loop concatenation for:
    • indentation/padding construction
    • recursive child text aggregation
  • Preserved existing formatting, including line breaks and pluralization behavior.

• Behavior-locking coverage

  • Added focused tests in TestToStringOutput to assert exact output strings for:
    • Path64
    • PathD
    • Paths64
    • PathsD
    • PolyPathBase (via PolyTree64)

// before
String s = "";
for (Point64 p : this) {
    s = s + p.toString() + " ";
}

// after
StringBuilder s = new StringBuilder();
for (Point64 p : this) {
    s.append(p.toString()).append(" ");
}
return s.toString();

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:

• jitpack.io
  • Triggering command: /usr/lib/jvm/temurin-17-jdk-amd64/bin/java /usr/lib/jvm/temurin-17-jdk-amd64/bin/java --enable-native-access=ALL-UNNAMED -classpath /usr/share/apache-maven-3.9.12/boot/plexus-classworlds-2.9.0.jar -Dclassworlds.conf=/usr/share/apache-maven-3.9.12/bin/m2.conf -Dmaven.home=/usr/share/apache-maven-3.9.12 -Dlibrary.jansi.path=/usr/share/apache-maven-3.9.12/lib/jansi-native -Dmaven.multiModuleProjectDirectory=/home/REDACTED/work/Clipper2-java/Clipper2-java org.codehaus.plexus.classworlds.launcher.Launcher test (dns block)
  • Triggering command: /usr/lib/jvm/temurin-17-jdk-amd64/bin/java /usr/lib/jvm/temurin-17-jdk-amd64/bin/java --enable-native-access=ALL-UNNAMED -classpath /usr/share/apache-maven-3.9.12/boot/plexus-classworlds-2.9.0.jar -Dclassworlds.conf=/usr/share/apache-maven-3.9.12/bin/m2.conf -Dmaven.home=/usr/share/apache-maven-3.9.12 -Dlibrary.jansi.path=/usr/share/apache-maven-3.9.12/lib/jansi-native -Dmaven.multiModuleProjectDirectory=/home/REDACTED/work/Clipper2-java/Clipper2-java org.codehaus.plexus.classworlds.launcher.Launcher -Dtest=TestToStringOutput test (dns block)
  • Triggering command: /usr/lib/jvm/temurin-17-jdk-amd64/bin/java /usr/lib/jvm/temurin-17-jdk-amd64/bin/java --enable-native-access=ALL-UNNAMED -classpath /usr/share/apache-maven-3.9.12/boot/plexus-classworlds-2.9.0.jar -Dclassworlds.conf=/usr/share/apache-maven-3.9.12/bin/m2.conf -Dmaven.home=/usr/share/apache-maven-3.9.12 -Dlibrary.jansi.path=/usr/share/apache-maven-3.9.12/lib/jansi-native -Dmaven.multiModuleProjectDirectory=/home/REDACTED/work/Clipper2-java/Clipper2-java org.codehaus.plexus.classworlds.launcher.Launcher -f pom.xml -B -V -e -Dfindbugs.skip -Dcheckstyle.skip -Dpmd.skip=true -Dspotbugs.skip -Denforcer.skip -Dmaven.javadoc.skip (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)

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