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/build/binary.rs

@@ -92,7 +92,7 @@ pub fn generate_binary_metadata(
     // ------------------------------------------------------------------
     let artifact_names: Vec<String> = files_list
         .iter()
-        .filter(|e| matches!(e.package_type.as_deref(), Some("deb") | Some("udeb")))
+        .filter(|e| e.is_binary_artifact())
         .map(|e| e.filename.clone())
         .collect();
 
@@ -159,16 +159,28 @@ pub fn generate_binary_metadata(
     // ------------------------------------------------------------------
     // Binary package names and descriptions
     // ------------------------------------------------------------------
+    // dpkg-genchanges lists only deb/udeb packages in `Binary:` (a ddeb
+    // is distributed through Files but is not a listed binary of the
+    // upload), while dpkg-genbuildinfo lists every binary artifact's
+    // package, ddebs included.
     let mut binaries: Vec<String> = Vec::new();
+    let mut buildinfo_binaries: Vec<String> = Vec::new();
     for name in &artifact_names {
-        if let Some(e) = files_list.get(name)
-            && let Some(pkg) = &e.package
-            && !binaries.contains(pkg)
-        {
+        let Some(e) = files_list.get(name) else {
+            continue;
+        };
+        let Some(pkg) = &e.package else {
+            continue;
+        };
+        if !buildinfo_binaries.contains(pkg) {
+            buildinfo_binaries.push(pkg.clone());
+        }
+        if e.package_type.as_deref() != Some("ddeb") && !binaries.contains(pkg) {
             binaries.push(pkg.clone());
         }
     }
     binaries.sort();
+    buildinfo_binaries.sort();
 
     // Description lines: first line of each binary stanza's Description,
     // formatted exactly like dpkg-genchanges, sorted.
@@ -238,7 +250,7 @@ pub fn generate_binary_metadata(
     let buildinfo_doc =
         crate::build::buildinfo::render_buildinfo(&crate::build::buildinfo::BuildInfoInput {
             source: source_display.clone(),
-            binaries: binaries.clone(),
+            binaries: buildinfo_binaries.clone(),
             architecture: buildinfo_arch_values.join(" "),
             version: entry.version.full(),
             binary_only_changes: binary_only_changes.clone(),