[C++] LevelDecoder::Decode，internal::FindMinMax consume lots of cpu

### Describe the bug, including details regarding any error messages, version, and platform.

[problem]
for a page with 6w int，when call record_reader->SkipRecords(59000);
it consume about 1.1ms

[why]
1) for a batch(1024), call FindMinMax, will compute 2048 times(1024 min, 1024 max)
2) 59000/1024=57 rounds

### Component(s)

C++