`decryptObjectInfo` is a significant bottleneck when listing objects.
Reduce the allocations for a significant speedup.
https://github.com/minio/sio/pull/40
```
λ benchcmp before.txt after.txt
benchmark old ns/op new ns/op delta
Benchmark_decryptObjectInfo-32 24260928 808656 -96.67%
benchmark old MB/s new MB/s speedup
Benchmark_decryptObjectInfo-32 0.04 1.24 31.00x
benchmark old allocs new allocs delta
Benchmark_decryptObjectInfo-32 75112 48996 -34.77%
benchmark old bytes new bytes delta
Benchmark_decryptObjectInfo-32 287694772 4228076 -98.53%
```
Design: https://gist.github.com/klauspost/025c09b48ed4a1293c917cecfabdf21c
Gist of improvements:
* Cross-server caching and listing will use the same data across servers and requests.
* Lists can be arbitrarily resumed at a constant speed.
* Metadata for all files scanned is stored for streaming retrieval.
* The existing bloom filters controlled by the crawler is used for validating caches.
* Concurrent requests for the same data (or parts of it) will not spawn additional walkers.
* Listing a subdirectory of an existing recursive cache will use the cache.
* All listing operations are fully streamable so the number of objects in a bucket no
longer dictates the amount of memory.
* Listings can be handled by any server within the cluster.
* Caches are cleaned up when out of date or superseded by a more recent one.
