Fix: Update RAG sample region to us-east1 and ADK to 1.31.0

[cnemri]

This PR updates the RAG sample to address a known vulnerability and update region requirements.

Changes:

1. Updated all references from us-central1 to us-east1 to align with Agent Garden deployment requirements.
2. Bumped google-adk dependency to version 1.31.0 and upgraded the uv.lock lockfile to resolve a known security vulnerability.
3. Added [eval] extra to the google-adk dependency to ensure evaluation dependencies are present.
4. Refactored the Arize evaluation script (test_eval_arize.py) to maintain functional equivalence while migrating to the newer Arize SDK (v8.x) API syntax (ArizeClient, arize_client.datasets.create, arize_client.experiments.run).