Add more testing for buildbox-tools

Description

This MR enhances the existing tests related to buildbox-tools by building all the tools under cpp and checking that casdownload successfully writes the metadata file when downloading actions. In addition, it also adds a new test using casupload and casdownload to upload/download a directory, basically same the test added in buildbox-tools CI in buildbox-tools!33

Note: This MR requires buildbox-tools!33 to be merged, so the CI will fail until then. If you want to test it locally you can update where buildbox-tools is cloned to point it to the santigl/dir-output-digest branch.