build/binary: native .buildinfo/.changes for binary builds (pkh deb)

Extend the metadata writers to binary-only uploads and wire them into
the 'pkh deb' flow:

- build/binary.rs generates <pkg>_<ver>_<arch>.buildinfo/.changes
  through any Context: debian/files consumption, encounter-order
  Architecture accumulation (sorted in .buildinfo like dpkg-genbuildinfo),
  sorted Binary lists, dpkg-formatted Description lines with udeb
  suffixes, Installed-Build-Depends closure over the context status DB,
  and binNMU handling (Source: pkg (prev), Binary-Only-Changes, previous
  .dsc redistribution);
- artifact digests are computed inside the context via coreutils
  (md5sum/sha1sum/sha256sum/stat) so chrooted/remote trees work;
- deb/local.rs runs the generation after 'rules binary', exports
  SOURCE_DATE_EPOCH from the changelog (reproducibility), and resolves
  vendor/profiles inside the context; deb/mod.rs retrieves the new
  artifacts alongside the debs;
- reusable helpers added: FilesList::parse/render,
  parse_changelog_entry_from_str, parse_previous_version_from_str,
  installed_build_depends_from_content.

Differential gate: same tree built with real 'dpkg-buildpackage -b' and
with the pkh flow; .changes/.buildinfo compared field-by-field modulo
machine-dependent fields, artifact checksums included.

src/deb/mod.rs

@@ -165,14 +165,18 @@ async fn build_binary_package_impl(
             }
         }
 
-        // Retrieve produced .deb files
+        // Retrieve produced artifacts (.deb files plus the upload metadata
+        // (.buildinfo/.changes) generated natively after the build)
         if let Some(u) = ui {
             u.phase(Phase::RetrievingArtifacts);
         }
         let remote_files = build_ctx.list_files(Path::new(&build_root))?;
         let deb_files: Vec<PathBuf> = remote_files
             .into_iter()
-            .filter(|f| f.extension().is_some_and(|ext| ext == "deb"))
+            .filter(|f| {
+                f.extension()
+                    .is_some_and(|ext| matches!(ext.to_str(), Some("deb") | Some("buildinfo") | Some("changes")))
+            })
             .collect();
         let total_debs = deb_files.len();