stmtctx: add mutex to protect stmtCache(#36159) (#36351)
stmtctx: add mutex to protect stmtCache(#36159) (#36351)

close pingcap/tidb#36159
pingcap/tidb,pingcap/tidb,pingcap/tidb,ngaut/tidb,ngaut/tidb,ngaut/tidb,pingcap/tidb,ngaut/tidb,ngaut/tidb,pingcap/tidb,ngaut/tidb,pingcap/tidb