Support github cache

Dear @aminya,

Thank you for providing this action. It is really helpful to me.

I would like to ask if there is any technical reason why github cache cannot be leveraged somehow to avoid re-installing the same packages every time. My pipelines run the same env for multiple jobs and sometimes setup-cpp is the step that takes most of the time (example: https://github.com/DiamonDinoia/finufft/actions/runs/13046204138/job/36416878122). Is it possible to cache the installations, or the resulting image entirely to avoid doing the same work all the time?

Thanks,
Marco

edit: if you can help me setting up custom docker images. I am happy to contribute to the documentation

No files or tests are named. Start by reviewing setup-cpp’s installation flow and GitHub Actions cache support, then determine whether package installations or resulting Docker images can be reused across jobs. Done means a supported caching or custom-image approach is documented and validated in a representative workflow.