Fix wrong metadata parsing in CompactOnExpiredCollector

[PragmaTwice]

The bug only affects users who enable the option ENABLE_NEW_ENCODING.

We fixed the metadata parsing (on expire time field) in CompactOnExpiredCollector.

Besides, we change the type of some timestamp from int to int64.

Unit test failed

[PragmaTwice]

Carry comment from @git-hulk in PragmaTwice#2 for better context:

RocksDB compaction allows to use of trivial move mode(move file into the next level instead of using compaction filter to generate the output file) when the compaction is not triggered by the manual way.

So after this fix, NeedCompact will return the correct result and then wait for the background compaction schedule(become no manual way so it allows the trivial move), so after we call the storage->Compact, it won't manually compact the moved file.

I fixed this issue by using force bottom-level compaction when triggering the manual compaction, it's our expected behavior.

See https://github.com/facebook/rocksdb/blob/ba597514309b686d8addb59616f067d5522186b7/db/db_impl/db_impl_compaction_flush.cc#L3358

[PragmaTwice]

Thanks all!