v6.5.3: feat(files): Consolidate mime type counts in backfill command output

The `files:fill-mime-type` command now aggregates the counts for each processed mime type across all internal batches. Previously, it would output a line for each batch.

This change ensures that the command's output is consolidated and cleaner, hiding the internal batching mechanism which is an implementation detail for query efficiency and should not be visible to the user.