7fe1ad1f63
Currently, make_and_start_task returns a pointer to task_manager::task that hides the implementation details. If we need to access the implementation (e.g. because we want a task to "return" a value), we need to make and start task step by step openly. Return task_manager::task::impl from make_and_start_task. Use it where possible. Fixes: https://github.com/scylladb/scylladb/issues/22146.