Reindex the existing vector index.
Issues a reindex (concurrently <bool>, verbose <bool>) index command
for the previously discovered or created index (tracked in
_embedding_index_name). The session-level index tuning GUCs
(returned by :meth:Algorithm.index_settings) are applied beforehand to
influence the reindex process (useful for algorithms whose maintenance
cost or accuracy depends on these settings).
:param concurrently: When True performs a concurrent reindex to
minimize locking, trading speed for availability.
:type concurrently: bool
:param verbose: When True enables PostgreSQL verbose output, which
may aid in diagnosing build performance issues.
:type verbose: bool
:return: True if reindex succeeded, False if no index existed.
:rtype: bool
:raises AssertionError: If embedding_index is unexpectedly None.
