Extending Cloud Service Support

To add a new spreadsheet backend implement the CloudSpreadsheetService trait. At minimum you must provide methods for creating a sheet, appending rows, reading rows and sharing the sheet with other users.

Once implemented you can optionally wrap the service with utilities such as BatchingCacheService for caching or RetryingService for resiliency.

Adapters are placed under src/cloud_adapters/ and re-exported in cloud_adapters::mod so that they can be used by the rest of the crate.