stop loading stats when has too much stats in the memory during the init stats

[hawkingrei]

Enhancement

During the initialization phase of TiDB, the system loads statistics into memory. However, when the volume of statistics is too large, it can lead to excessive memory usage, causing performance degradation or even out-of-memory errors.

Currently, TiDB does not have a mechanism to stop loading statistics when there are too many stats in memory during the initialization phase. This can lead to significant memory consumption, impacting the stability and performance of the system.