Internal helper function to retry reading a key from the system keyring. This handles potential intermittent delays after writing to the keyring.
.retry_key_get(service, username, retries = 5, delay = 0.5)
Character scalar. The retrieved credential value. Will throw an error if unable to retrieve a valid, non-blank value after all retries.
Character. Keyring service name (e.g., "valdr_credentials").
Character. Keyring username (e.g., "client_id").
Integer. Number of retry attempts before giving up (default 5).
Numeric. Delay in seconds between retry attempts (default 0.5).