Fix post-merge CI on MSVC x86_64
gen-cache: Use bzip2 instead of xz on Windows
Compressing the deps cache with xz seems to cause hangs on the Windows
CI, so let's use bzip2. The size difference is minimal on Windows
anyway, but it's quite significant on other platforms.
gen-cache: Add files verbosely for debugging reasons
This way we get progress status to debug hangs and we can also easily
inspect changes in the contents, or extraneous files that should not
be cached.
gen-cache: Sprinkle some more logging
This helps debug issues with cache generation on the CI