We hit an i/o performance bottleneck when executing
fdroid update on our fdroidserver. We have a lot of APKs that are rather large, so calculating the sha256sum of each one takes a long time.
This change adds a cli flag
The default is to keep the existing behaviour of calculating the sha256sum when verifying the cache.
If the flag is specified, the cache is verified using the file modification timestamp and size in bytes.
Because a new apk attribute
mtime was added, the cache will read as stale for all existing APKs when the flag is first enabled.