build(deps): Migrate Google ADK and ADK-A2A from v0.9.0 to v1.5.0

[theyihlin]

Summary

This PR upgrades the google-adk and google-adk-a2a dependencies to the latest stable version 1.5.0, keeping the A2UI Kotlin SDK aligned with the latest ADK specification and capabilities. Per the integration plan, the a2a-java-sdk-client dependency remains untouched at 1.0.0.Alpha3.

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Key Changes

1. Dependency Upgrades

• Bumps com.google.adk:google-adk and com.google.adk:google-adk-a2a to 1.5.0 in:
  • agent_sdks/kotlin/build.gradle.kts
  • samples/community/agent/adk/rizzcharts/java/build.gradle.kts
  • samples/community/agent/adk/rizzcharts/kotlin/build.gradle.kts

2. Session Lifecycle Refactoring (SessionKey Integration)

• Refactored A2aHandler to construct the SessionKey at the very beginning of the RPC handling block.
• Passed this SessionKey directly to a refined getOrCreateSession(sessionKey) method and to runner.runAsync(...). This unifies the lifecycle around SessionKey and removes parameter duplication.
• Adapted getOrCreateSession to utilize the new ADK v1.5.0 two-parameter signature: getSession(SessionKey, GetSessionConfig?) passing null for the config, which replaces the legacy Java Optional wrapper.

3. Test Suite Adjustments

• A2aConformanceTest.kt: Updated the mock runner expectations to match the new SessionKey and two-parameter getSession signatures.
• AdkExtensionsConformanceTest.kt: Added mock stubbing for Part.partMetadata() on the mocked GenAI Part object to prevent MockKException caused by internal calls inside the new ADK v1.5.0 event converter.

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Verification

• Formatted all modified Kotlin source and test files using ktfmt.
• Successfully compiled and ran the full Kotlin SDK test suite, with all 216 tests passing:

  $ ./gradlew test
  ...
  BUILD SUCCESSFUL in 7s

[gemini-code-assist]

Code Review

This pull request upgrades the Google ADK dependency from version 0.9.0 to 1.5.0 across multiple build files and refactors session management in A2aHandler to use SessionKey instead of individual string parameters. Feedback suggests using Kotlin's Elvis operator (?:) in getOrCreateSession to simplify the control flow and avoid mutable variables.