Benchmarks don't test reading Zarr v2 format #3757
Description
None of the benchmarks in this repo appear to benchmark reading zarr v2 format data. This means that the v2 to v3 compatibility layer, including the special v2 codec wrapper, is not benchmarked (note this uses asyncio.to_thread).
This appears to have led to this significant performance regression in a basic indexing workload.
We should add v2 format to the benchmarks, and make sure its just as fast as v3 (there is no reason why it shouldn't be as far as I'm aware).