nfpm re-renders semver versions into the RPM filename, so `2025.08.03` ships as `2025.8.3`. The existence probe asked artifactapi for the raw metadata version, always got a 404, and rebuilt and republished `nzbget_exporter` and `unkin-ca-certificates` on every pipeline run.
- add `nfpm_rpm_version`/`rpm_file_name` mirroring nfpm rendering
- build the probe filename through `rpm_file_name`
- drop dead `normalize_version` and `get_package_full_name`
- cover the nfpm rendering table and the probed URL in tests
Reviewed-on: #175
Co-authored-by: unkin-agent <unkin-agent@unkin.net>
Co-committed-by: unkin-agent <unkin-agent@unkin.net>