Set up tmt test plans and Testing Farm integration

Integrate tmt (Test Management Tool) and Testing Farm for test orchestration across multiple platforms and Fedora versions.

## Tasks

- Create `plans/` directory with tmt test plans
- Create `.fmf/version` file to enable FMF
- Add FMF metadata to tests
- Create GitHub Actions workflow for Testing Farm integration
- Test on multiple Fedora versions (43, 44, Rawhide) and architectures (x86_64, aarch64)

## Acceptance Criteria

- `tmt run` executes tests locally
- Testing Farm runs tests on PRs
- Test results visible in GitHub PR checks
- Test cases are run on Testing Farm public ranch

## Dependencies

- Depends on #35 (pkg/tar-diff tests)
- Depends on #36 (pkg/tar-patch tests)
- Depends on #37 (pkg/common tests)