Extend `vertexAccessToken` to support proxy-aware HTTP clients and update calls accordingly for better configurability. Add `deleteTokenRecord` to handle token cleanup, improving management of authentication files.
Introduce Vertex AI Gemini integration with support for service account-based authentication, credential storage, and import functionality. Added new executor for Vertex AI requests, including execution and streaming paths, and integrated it into the core manager. Enhanced CLI with `--vertex-import` flag for importing service account keys.