infoschema v2:High memory usage caused by partition table metadata

## Enhancement
When the cluster contains a large number of partition tables, and there are frequent DDL operations on non-partition tables.infoschema consumes excessive memory.
When the cluster contains 160k partitions, the memory usage reaches about 55 GB。

Start by reproducing the reported case with 160k partitions and frequent DDL operations on non-partition tables, then inspect infoschema's partition table metadata handling. Done means identifying and addressing the excessive memory use while preserving the reported infoschema behavior and verifying that memory no longer approaches 55 GB in the same scenario.

Written by the indexing model from the issue text.