doc: add docstring and do some refactor

packer/src/sarasacw_omrf_packer/archiver.py

@@ -1,3 +1,9 @@
+"""Dual-sink archiver that materializes a distribution tree.
+
+The :class:`Archiver` mirrors the same logical entries into an on-disk
+directory and/or a zip archive, and is usable as a context manager.
+"""
+
 import zipfile
 import shutil
 from pathlib import Path
@@ -43,6 +49,11 @@ class Archiver:
             self.__dist_zip = None
 
     def push_dir(self, arcname: Path) -> None:
+        """Create an empty directory entry in both sinks.
+
+        :param arcname: Directory path relative to the distribution root.
+            Parent directories are created as needed for the directory sink.
+        """
         if self.__dist_dir is not None:
             target_filepath = self.__dist_dir / arcname
             target_filepath.parent.mkdir(parents=True, exist_ok=True)