Add robust type validation and error interception for gfi responses

[JoseRLopezE]

This PR introduces a new helper function, handleGfiResponse, to centralize and improve type validation and error handling for responses from the gfi function.

Ensures only valid arrays are processed, throwing clear errors for string error messages or unexpected response types. Handles empty results gracefully with user-friendly messages. Prepares the codebase for better testability and future maintenance. Includes unit tests to verify all edge cases and error paths. This change improves the reliability and user experience of the CLI when interacting with the GitHub API.