Returns the block hash for the canonical block at the given number.

        Raises BlockNotFound if there's no block header with the given number in the
        canonical chain.

def get_canonical_block_hash(self, block_number: BlockNumber) -> Hash32:
        """
        Returns the block hash for the canonical block at the given number.

        Raises BlockNotFound if there's no block header with the given number in the
        canonical chain.
        """
        return self._get_canonical_block_hash(self.db, block_number)