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/debian/changelog.rs

@@ -46,7 +46,15 @@ pub fn parse_changelog_entry(path: &Path) -> Result<ChangelogEntry, Box<dyn std:
             e
         )
     })?;
+    parse_changelog_entry_from_str(&content)
+}
 
+/// Parse the most recent changelog entry from its textual content. `origin`
+/// is used in error messages only.
+pub fn parse_changelog_entry_from_str(
+    content: &str,
+) -> Result<ChangelogEntry, Box<dyn std::error::Error>> {
+    let origin = "changelog";
     let mut lines = content.lines().peekable();
 
     // --- Header line: `package (version) distributions; urgency=medium[, key=value]`
@@ -55,17 +63,13 @@ pub fn parse_changelog_entry(path: &Path) -> Result<ChangelogEntry, Box<dyn std:
             Some(l) if l.trim().is_empty() => continue,
             Some(l) => break l.trim_end(),
             None => {
-                return Err(format!("changelog '{}' is empty", path.display()).into());
+                return Err(format!("changelog '{origin}' is empty").into());
             }
         }
     };
 
     let open = header.find('(').ok_or_else(|| {
-        format!(
-            "invalid changelog header in '{}': {}",
-            path.display(),
-            header
-        )
+        format!("invalid changelog header in '{origin}': {header}")
     })?;
     let close = header[open..]
         .find(')')
@@ -123,9 +127,8 @@ pub fn parse_changelog_entry(path: &Path) -> Result<ChangelogEntry, Box<dyn std:
 
     let trailer_line = trailer.ok_or_else(|| {
         format!(
-            "no maintainer trailer found in '{}': expected a line of the form \
-             ' -- Name <email>  Date'",
-            path.display()
+            "no maintainer trailer found in '{origin}': expected a line of the form \
+             ' -- Name <email>  Date'"
         )
     })?;
 
@@ -148,12 +151,7 @@ pub fn parse_changelog_entry(path: &Path) -> Result<ChangelogEntry, Box<dyn std:
 
     let timestamp = DateTime::parse_from_rfc2822(&date_raw)
         .map_err(|e| {
-            format!(
-                "cannot parse changelog date '{}' in '{}': {}",
-                date_raw,
-                path.display(),
-                e
-            )
+            format!("cannot parse changelog date '{date_raw}' in '{origin}': {e}")
         })?
         .timestamp();
 
@@ -220,7 +218,14 @@ fn find_closes(body_lines: &[String]) -> Option<String> {
 pub fn parse_previous_version(path: &Path) -> Result<Option<String>, Box<dyn std::error::Error>> {
     let content = std::fs::read_to_string(path)
         .map_err(|e| format!("failed to read changelog '{}': {}", path.display(), e))?;
+    parse_previous_version_from_str(&content)
+}
 
+/// Return the version of the *previous* changelog entry from the textual
+/// content of a changelog file.
+pub fn parse_previous_version_from_str(
+    content: &str,
+) -> Result<Option<String>, Box<dyn std::error::Error>> {
     let mut seen_first = false;
     for line in content.lines() {
         let line = line.trim_end();
@@ -229,12 +234,12 @@ pub fn parse_previous_version(path: &Path) -> Result<Option<String>, Box<dyn std
                 seen_first = true;
                 continue;
             }
-            let open = line.find('(').ok_or_else(|| {
-                format!("invalid changelog header in '{}': {}", path.display(), line)
-            })?;
+            let open = line
+                .find('(')
+                .ok_or_else(|| format!("invalid changelog header: {line}"))?;
             let close = line[open..]
                 .find(')')
-                .ok_or_else(|| format!("unbalanced parenthesis in changelog header '{}'", line))?;
+                .ok_or_else(|| format!("unbalanced parenthesis in changelog header '{line}'"))?;
             return Ok(Some(line[open + 1..open + close].to_string()));
         }
     }