feat: avoid sst compacat twice

[crwen]

#151

• Add a compact status to avoid sst compact twice
• Modify LevelStream::new declaration to accept needed data only
• remove range index returned by this_level_scopes and next_level_scopes

[KKould]

Is this retain meet_scopes_l? Because there will be no new sstable in meet_scopes_ll because compaction will increase step by step at level.

[crwen]

It should be meet_scopes_ll. Because we only care sstables that may be compacted in next compaction loop

[KKould]

The meet_scopes_ll of this compaction is the meet_scopes_l of the next compaction, right?

[crwen]

Yes, meet_scopes_l also need filtering, but it needn't insert to compact_status. So the code may be like this:

meet_scopes_l.retain(|scope| !compact_status.contains(&scope.gen));
meet_scopes_ll.iter().for_each(|scope| {
    compact_status.insert(scope.gen);
});

[KKould]

I'm not sure if compact_status requires both meet_scopes_ll to be inserted, new sstables are ignored here, and is it better to just insert new sstables?

[KKould]

It looks like the unit test is missing to verify that it is working properly