Method PurgeTrashAsync(long, int, int, IProgress<PurgeProgress>?, CancellationToken)

Purge a trash container created by SoftDeleteAsync.
Physically deletes objects in batches with progress callback.
Call this after SoftDeleteAsync if you want to control purge timing separately.

Task PurgeTrashAsync(long trashId, int totalCount, int batchSize = 10, IProgress<PurgeProgress>? progress = null, CancellationToken cancellationToken = default)