rust: mostly avoid streaming zstd decompression
Streaming ZStd decompression seems slightly slower, and
the API we use makes it very inconvenient to re-use the
decompression context.
Instead of using that, use the buffer-backed version,
because we can give a reasonable-ish size estimate.
This directory is meant to cache artifacts useful for tests (such as bundle).
Those artifacts need to be cached because they are slow to regenerate on each
test but too large to be tracked within the repository. They are not expected
to change between each run and can be cached.
The `./scripts/` contains code to generate the artifact while the `cache`
directory contains resulting artifact.