Returns the requested block header as specified by block hash.

        Raises BlockNotFound if there's no block header with the given hash in the db.

def get_block_header_by_hash(self, block_hash: Hash32) -> BlockHeader:
        """
        Returns the requested block header as specified by block hash.

        Raises BlockNotFound if there's no block header with the given hash in the db.
        """
        validate_word(block_hash, title="Block Hash")
        return self.chaindb.get_block_header_by_hash(block_hash)