Leowner

feat: add disktable status

5

* **What kind of change does this PR introduce?** (Bug fix, feature, docs update, ...) Add SchedGC, GetRecordPkCnt and GetRecordIdxCnt in disktable

Wrong results in Memtable::GetRecordIdxCnt

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Wrong results in Memtable::GetRecordIdxCnt. 1. Here `GetRecordIdxCnt` will get RecordIdxCnt for `idx`. But inside this function, it will call `segments_[real_idx][i]->GetIdxCnt();`. Maybe `int GetIdxCnt(uint32_t ts_idx, uint64_t& ts_cnt)` should be used instead...