CI Testing Programs & Upstream Integration for OpenPrinting

This project establishes a comprehensive, automated Continuous Integration (CI) and testing infrastructure across five core OpenPrinting repositories (libppd, libpappl-retrofit, libcupsfilters, cups-filters, and cups-snap). Phase 1 focuses on writing native, standalone C unit tests for libppd and libpappl-retrofit utilizing Michael Sweet’s minimalist testing paradigm to achieve robust make check coverage. Phase 2 engineers a novel "DESTDIR Staging" architecture to upstream downstream Debian/Ubuntu autopkgtests directly into GitHub Actions. This allows complex system-integration tests to execute locally on every commit without host pollution, guaranteeing legacy driver compatibility and instantly catching regressions across native and QEMU-emulated architectures