Function process_mapping_command 

pub fn process_mapping_command<S: BlockService + ?Sized + 'static, D: DeliveryHandler>(
    msg: &Message<'_, RawMappingCommand>,
    files: &Arc<Files<S, D>>,
) -> Result<(), Error>

Processes a raw mapping command (RawMappingCommand), decoding extent descriptors, reading blob metadata from storage, registering Merkle leaves via files, and inserting/removing the file from files.