Optimizes reading multiple chunks from a shard. Reads of nearby chunks within the same shard are coalesced to reduce the number of calls to the store. After any coalescing, the resulting byte ranges are read in parallel.
Coalescing respects two config options. Reads are coalesced if there are fewer
than sharding.read.coalesce_max_gap_bytes bytes between chunks and the total
size of the coalesced read is no more than sharding.read.coalesce_max_bytes.