Update Gradle wrapper to 9.2.1 and resolve pmd issues

[haroon-sheikh]

This pull request updates the Gauge Gradle plugin to version 3.1.0 and introduces several improvements and cleanups to the plugin codebase and its tests. The most significant changes include updating dependencies and Gradle versions, refactoring code for clarity and maintainability, and improving test conventions.

Dependency and Version Updates:

• Upgraded the Gauge Gradle plugin version from 2.1.0 to 3.1.0 in the README.md, build.gradle example, and plugin/gradle.properties.
• Updated the Gradle wrapper to use version 9.2.1 (was 8.14.3) and updated the distribution SHA256 checksum accordingly in gradle-wrapper.properties.

Codebase Improvements and Refactoring:

• Refactored task classes (AbstractGaugeTask, GaugeClasspathTask, GaugeTask, GaugeValidateTask) to use super for setting group, description, and dependencies, and to pass descriptions via constructors for clarity.
• Made GaugeConstants a final class and added a private constructor to prevent instantiation.
• Cleaned up and simplified the GaugeCommand class by removing unnecessary imports, streamlining flag logic, and using toList() instead of Collectors.toList().
• Moved default property conventions for the GaugeExtension from the class constructor to the plugin application logic in GaugePlugin, improving separation of concerns.

Test and Example Code Improvements:

• Updated integration and unit test classes to use package-private class and method visibility (removing public), reordered imports, and improved code style for consistency.
• Enhanced the test project plugin application block to use a multi-line string and set failOnNoDiscoveredTests = false for test tasks.

Build Script and Wrapper Cleanup:

• Removed unused or redundant CLASSPATH assignments in gradlew and gradlew.bat scripts.
• Updated copyright year in gradlew.

These changes collectively modernize the plugin, improve maintainability, and ensure compatibility with the latest Gradle and Gauge versions.

[gaugebot]

@haroon-sheikh Thank you for contributing to gauge-gradle-plugin. Your pull request has been labeled as a release candidate 🎉🎉.

Merging this PR will trigger a release.

Please bump up the version as part of this PR.

Instructions to bump the version can found at CONTRIBUTING.md

If the CONTRIBUTING.md file does not exist or does not include instructions about bumping up the version, please looks previous commits in git history to see what changes need to be done.