[storage]: add helpers for the rewrite loop

The `rewriteObject()` request typically is used in a loop, as it may require multiple calls before completing. Interestingly, it does **not** make progress in the background, the call is needed.

We can add a helper function to run the loop, maybe via some `extension` of the `StorageControlProtocol`.

Start by locating the `rewriteObject()` request and the `StorageControlProtocol` definition, then trace how callers currently repeat the request until completion. Determine the helper's intended API and completion behavior with the project maintainers; done means the loop can be invoked through the chosen protocol extension and is covered by the relevant tests.

Written by the indexing model from the issue text.