Avoid duplicate pkl-gradle publication

[RushikeshGandhmal]

Summary

• stop applying pklPublishLibrary to pkl-gradle, since java-gradle-plugin already creates the pluginMaven publication
• retain the shared POM metadata, validation, signing, and archive-artifact configuration without creating a duplicate publication
• allow POM validation to target pluginMaven while preserving the existing library default

java-gradle-plugin creates pluginMaven from the Java component. Applying pklPublishLibrary created a second library publication from that same component with the same coordinates, causing the Sonatype overwrite warning.

This is a fresh submission of #1761 following the reviewer invitation to resubmit.

Fixes #1742

Verification

• reproduced the duplicate on a clean upstream main checkout by confirming identical library and pluginMaven POMs and both Sonatype publication tasks
• ./gradlew :pkl-gradle:clean :pkl-gradle:validatePom :pkl-gradle:build :pkl-core:validatePom :pkl-bom:validatePom :stdlib:validatePom --no-build-cache --console=plain
• ./gradlew :pkl-gradle:publishToSonatype --dry-run --console=plain
• confirmed the pluginMaven POM is generated and the duplicate library POM is absent
• confirmed the dry run schedules only pluginMaven and the required pklPluginMarkerMaven publication
• confirmed signing tasks remain for both publications
• compared pluginMaven module metadata with the baseline and confirmed the main, sources, and Javadoc publication artifacts are unchanged
• confirmed the legacy archives variant still contains the main, sources, and Javadoc JARs
• ./gradlew :pkl-gradle:spotlessCheck
• git diff --check

[RushikeshGandhmal]

Hi @bioball,

I manually reproduced the behavior described in #1742.

Before the fix, the generated POMs for the library and pluginMaven publications had identical SHA-256 hashes. A Sonatype dry run also scheduled both publication tasks:

• publishLibraryPublicationToSonatypeRepository
• publishPluginMavenPublicationToSonatypeRepository

This reproduced the duplicate publication reported in the issue. No artifacts were uploaded because publication was tested with --dry-run.

I then repeated the verification on the current PR head, 5c9cc958.

After the fix:

• The pkl-gradle tests and build pass.
• generatePomFileForPluginMavenPublication runs successfully.
• The pluginMaven POM is generated and validated.
• No duplicate library POM is generated.
• The Sonatype dry run schedules only pluginMaven and the required pklPluginMarkerMaven publication.

No artifacts were uploaded during these checks.

[RushikeshGandhmal]

pklPublishLibrary also added the sources and Javadoc JARs to the legacy archives configuration. Since pkl-gradle no longer applies that convention, this block preserves the existing archive behavior without recreating the duplicate library publication.