fix(mvcc): fix commit xid may be accidentally reused #26
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问题： 在事务恢复阶段，
MTR_BEGIN日志对应的 trx id 会在MvccTrxManager类的create_trx(int32_t trx_id)方法中更新current_trx_id以避免重复使用，符合预期。但是MTR_COMMIT日志所使用的 commit xid 没有更新，可能会被重用而导致错误的结果。解决方案： 增加
update_trx_id方法用于确保current_trx_id不小于给定的参数。在 recover 阶段，MvccTrx提交时应当调用该方法更新current_trx_id。