cache static-php-cli builds and reuse them across workflows

[henderkes]

Describe you feature request

Is your feature request related to a problem? Please describe. The run times for the pr CI workflows are very long,

Describe the solution you'd like Run a job that runs once a day, initialises our static-builder Dockerfiles and uploads the whole dist/static-php/buildroot folder. In subsequent workflows, check if prebuilt-frankenphp-spc-2025-04-15.tar.gz exists as a download, if it does, download that and skip the spc download and build step.

Describe alternatives you've considered We could do this on the static-php side, but since the collection of preselected extensions and libraries is rather unique to frankenphp, I think it's better to do it here.