Fix Gradle deprecation warnings for Gradle 9.0 compatibility

[Copilot]

This PR addresses all Gradle deprecation warnings that would make the build incompatible with Gradle 9.0.

Changes Made

1. Fixed buildDir deprecation

Replaced deprecated $buildDir property with ${layout.buildDirectory.get()} in:

• agent/agent/build.gradle.kts
• agent/agent-for-testing/build.gradle.kts
• buildSrc/src/main/kotlin/ai.javaagent-instrumentation.gradle.kts
• buildSrc/src/main/kotlin/ai.sdk-version-file.gradle.kts

2. Fixed archivesBaseName deprecation

Replaced deprecated archivesBaseName with base.archivesName in:

• etw/java/build.gradle

3. Fixed Spotless configuration deprecation

Replaced deprecated indentWithSpaces() with leadingTabsToSpaces() in:

• buildSrc/src/main/kotlin/ai.spotless-conventions.gradle.kts

4. Fixed task creation deprecation

Replaced deprecated task<Test>() with tasks.register<Test>() in:

• buildSrc/src/main/kotlin/ai.smoke-test.gradle.kts

5. Removed deprecated system property

Removed systemProp.org.gradle.kotlin.dsl.precompiled.accessors.strict=true from gradle.properties as this property is now deprecated and defaults to true.

6. Updated plugin versions

Updated plugins to eliminate deprecated Convention API usage:

• Spring Boot plugin: 2.5.12 → 2.7.18
• Protobuf plugin: 0.8.19 → 0.9.4

Testing

✅ Build passes with --warning-mode all and produces zero deprecation warnings
✅ Agent assembly works correctly
✅ All affected modules build successfully
✅ No functional changes to existing behavior

The build is now fully compatible with Gradle 9.0.

Fixes #74.

---

💡 You can make Copilot smarter by setting up custom instructions, customizing its development environment and configuring Model Context Protocol (MCP) servers. Learn more Copilot coding agent tips in the docs.