We should get rid of the gpu id dir too as it will never get cleaned up
should a user upgrade their gpu or copy their home dir to a new PC.
We also need to write the timestamp and gpu id to the header of each
cache entry (like we do with the filesize). This will be used for the
collection and
Instead of using a directory, hash the timestamps into the cache keys
themselves. Since there is no more timestamp directory, there is no more
need for deleting the cache of other mesa versions and we rely on
eviction to clean up the old cache entries. This solves the problem of
using several incar
