deb,build: export ddebs from binary builds

dh_strip registers debug-symbol packages in debian/files under their
renamed .ddeb name; they are deliverables of the build just like the
regular .debs. Both artifact-type filters, the one collecting the
build's artifacts and the one feeding the .buildinfo/.changes
checksum sections, accepted only deb and udeb, so every ddeb a build
produced was silently discarded: nothing exported next to the .debs,
nothing in the upload metadata.

The filter is now a shared FilesEntry::is_binary_artifact() predicate
(plus unit tests) used by both call sites, so the two cannot drift
apart again.

One dpkg distinction has to be copied rather than shared:
dpkg-genchanges lists only deb/udeb packages in the changes' Binary:
and Description (a ddeb travels in Files and the checksum sections
but is not a listed binary of the upload), while dpkg-genbuildinfo
lists every binary artifact's package, ddebs included. The package
list is therefore accumulated twice, once per consumer.

The binary-metadata differential fixture gains a Package-Type: ddeb
package, so the native .changes/.buildinfo generation is compared
against real dpkg with a ddeb present. Without the fix the comparison
fails on the checksum sections (golden distributes the ddeb, ours
dropped it); with it every field matches.

src/deb/local.rs

@@ -939,7 +939,7 @@ fn collect_binary_artifacts(
     let upload_dir = Path::new(build_root);
     let mut artifacts = Vec::new();
     for entry in files_list.iter() {
-        if matches!(entry.package_type.as_deref(), Some("deb") | Some("udeb")) {
+        if entry.is_binary_artifact() {
             artifacts.push(upload_dir.join(&entry.filename));
         }
     }