Add build reverse dependencies job using ratt

This allows maintainers to build reverse dependencies of their package in Salsa CI, useful for transitions, library updates, and catching regressions early.

• Add artifacts of the logs (since some jobs can exceed the default artifact size limit)
• Implement some logic to exclude packages marked with FTBFS from the build process to save time and resources
• Support multiple Debian releases
• Finalize and update the open PR for ratt to target Debian unstable as soon as possible.
• Add tests in the pipeline
• Improve the commits structure
• Only build direct reverse dependencies
• Add support in chdist for handling extra repositories correctly (for instance for: stable, oldstable and experimental).

⚠️ Build reverse dependencies jobs are disabled by default and must be triggered on demand (not on every push). To protect Salsa’s infrastructure, there is a hard cap of 100 reverse dependencies per pipeline. This ensures no single package overloads the runners.

Closes: #178 (closed)