Function process 

pub fn process<S, P, B, BB, BH>(
    meta: &(impl EraMeta + ?Sized),
    writer: &mut StaticFileProviderRWRefMut<'_, <P as NodePrimitivesProvider>::Primitives>,
    provider: &P,
    hash_collector: &mut Collector<BlockHash, BlockNumber>,
    block_numbers: impl RangeBounds<BlockNumber>,
) -> Result<BlockNumber>
where
    S: EraBlockReader<BH, BB>,
    B: Block<Header = BH, Body = BB>,
    BH: FullBlockHeader + Value,
    BB: FullBlockBody<Transaction = <<P as NodePrimitivesProvider>::Primitives as NodePrimitives>::SignedTx, OmmerHeader = BH>,
    P: DBProvider<Tx: DbTxMut> + NodePrimitivesProvider + BlockWriter<Block = B>,
    <P as NodePrimitivesProvider>::Primitives: NodePrimitives<BlockHeader = BH, BlockBody = BB>,

Reads meta with the EraBlockReader S, appends its blocks within block_numbers, and marks meta processed if the file was fully consumed. Returns last block height.