Cache multiple zstd frames in CompressedCarV1BackedBlockstore

[aatifsyed]

We currently only cache one zstd frame:

forest/src/car_backed_blockstore.rs

Line 335 in 79a1fd9

most_recent_zstd_frame: Option<(u64, std::io::Cursor<Vec<u8>>)>,

But

executing tipsets is roughly 5x slower with compressed snapshots than without on my machine. A cache of decoded frames should close that gap, though.

• @lemmih, in slack

We should cache more frames and see if that helps.

[lemmih]

Note that we eventually want multiple CAR files sharing a single cache.

[lemmih]

It doesn't make sense to work on this until the CAR store has matured. Otherwise, it'll just have to be rewritten.

[lemmih]

Closed by #3288