File Read with MMAP
https://forums.swift.org/t/what-is-the-best-way-to-work-with-the-file-system/71020/18
This post suggests that we can read from files ~20% faster using mmap instead of fread(), and I'm thinking this is particularly relevant in the ZSTD sections of code. Right now, that code seems to be CPU-constrained, so I'm not sure that we would see any performance improvement, but it's a fairly simple change to move to mmap if the need arises.
Worth exploring when time permits.