This seems to be much more space-efficient: ~/.cache/nix/tarball-cache
is about 700MiB uncompressed, under 300MiB as tzst (using tar's
defaults, CI uses zstdmt but I assume will be in the same ballpark). The
gitv3 cache is multiple GiB.
CI will still build doom-example using fetchGit. I intend to shrink the
number of modules enabled in the example to keep gitv3 cache size under
control.
