Add RAG-based memory for build-error fixes

## Current status and purpose This is a new draft PR that sets up controlled experiments for evaluating a Cloud SQL-backed error-memory system in OSS-Fuzz-Gen. The immediate purpose is to verify that the memory utilities can authenticate and connect to the experimental Cloud SQL instance from the CI/CD environment, and to exercise the complete retrieval and online-update workflow. This PR is not ready for review or merge. The implementation and configuration may change based on the experimental results.