code: def _add_block_number_to_hash_lookup(db: BaseDB, header: BlockHeader) -> None:
          
          block_number_to_hash_key = SchemaV1.make_block_number_to_hash_lookup_key(
              header.block_number
          )
          db.set(
              block_number_to_hash_key,
              rlp.encode(header.hash, sedes=rlp.sedes.binary),
          )
docs: Sets a record in the database to allow looking up this header by its
          block number.