cache uncompressed chunks

[toloudis]

Use Case

The current chunk cache stores the fetched blobs in cache. These chunks are typically compressed. Whenever we have a cache hit, we have to pay for decompression every time.
One way we can make playback mode faster is to store chunks decompressed.
Accept a cost of memory consumption, for the tradeoff of faster cache hits at run time.

Solution

We use a Store class that inherits from Zarrita's Store.
We preliminarily think this might require forking Zarrita to add the hooks or expose the internal modules we need.

Measure performance before and after.