Support new rst hash format (xxh3)

[Morilli]

Starting with pbe patch 14.15, rst hashes now use xxh3 instead of xxh64.

I've modified the code in a similar way to the existing bin type handling, as sadly riot did not care to update the rst file version to signal the updated hashing method.

Main TODO: Decide how to handle hashes.

Currently my idea is to have a legacy hashfile containing xxh64 hashes and a new hashfile containing xxh3 hashes. That allows for backwards compatibility in parsing and converting stringtable files from before patch 14.15 using that legacy hashfile. Current names are temporary; not entirely sure how to name them. some ideas: hashes.rstlegacy.txt - hashes.rst.txt hashes.rst.xxh64.txt - hashes.rst.xxh3.txt

[benoitryder]

I like the hashes.rst.xxh64.txt/hashes.rst.xxh3.txt option. It's nice to have explicit names. Moreover, "legacy" would not work if it changes again.