feature: support caching of signature databases

[sebthom]

It would be great if GHA caching could be provided for bytecode.cvd, main.cvd and on windows for the exe installer file. This reduces installation time, load on external systems and gives some level of protection from external systems being offline.

At least on Linux it seems you can manually install the CVD files (i.e. load them from the cache) https://askubuntu.com/questions/1046700/how-do-i-manually-import-the-clamav-virus-definition-file