Enable build caching for GwtCompileTask

[jiakuan]

Summary

Enable build caching for GWT compilation tasks by adding the @CacheableTask annotation. This allows Gradle to cache and reuse compilation outputs when inputs haven't changed, significantly improving build performance.

• Adds @CacheableTask annotation to GwtCompileTask
• No changes to task behavior - only enables caching capability
• All required inputs and outputs were already properly annotated

Impact

• Performance improvement: GWT compilation can be skipped when inputs haven't changed (saves up to 6 minutes per build as reported in Could GwtCompileTask be @CacheableTask ? #106)
• Better developer experience: Faster incremental builds when working on backend-only changes
• CI optimization: Cached outputs can be shared across builds and machines with remote cache

[Copilot]

Pull Request Overview

This PR enables build caching for GWT compilation tasks by adding the @CacheableTask annotation to improve build performance. The change allows Gradle to cache and reuse compilation outputs when inputs haven't changed, potentially saving significant compilation time.

• Adds @CacheableTask annotation to enable Gradle build caching
• Imports the required CacheableTask class
• No functional changes to the task behavior

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[lefevre00]

This is awesome, my build - including docker image build - run now in 2m20s
Caching output for this task allowed using caches for every next tasks