- Decoupled Google Sheets API interaction into `GoogleSheetsClient`.
- Decoupled OAuth2 device code flow logic and state into `DeviceAuthProvider`.
- Refactored `sheets.service.ts` to use these new components while maintaining the existing public API.
- Added comprehensive unit tests for `GoogleSheetsClient` and `DeviceAuthProvider`.
- Improved type safety by using `OAuth2Client` instead of `any`.
- Ensured consistency with original behavior by including `responseRanges` in `batchUpdate`.
Co-authored-by: cpvalente <34649812+cpvalente@users.noreply.github.com>