package.debian: Re-implement debian loader within the package loader mechanism

This introduces the debian package loader.

Contrary to other package loaders, a package can have multiple artifacts (per package version).

In those terms, we had to slightly adapt the swh.loader.package.loader.PackageLoader to demonstrate this. Thus the impacts on pypi, npm, deposit modules as well.

Related #2025 (closed) Related swh-core!91 (closed) Related swh-lister!114 (closed)

Test Plan

tox

---

Migrated from D2135 (view on Phabricator)

swh/loader/package/tests/test_debian.py

@@ -269,13 +269,15 @@ def test_get_package_metadata(requests_mock_datadir, datadir, tmp_path):
     logger.debug('package: %s', package)
 
     # download the packages
-    download_package(package, tmp_path)
+    all_hashes = download_package(package, tmp_path)
 
     # Retrieve information from package
     _, dsc_name = dsc_information(package)
 
+    dl_artifacts = [(tmp_path, hashes) for hashes in all_hashes.values()]
+
     # Extract information from package
-    extracted_path = extract_package(package, tmp_path)
+    extracted_path = extract_package(dl_artifacts, tmp_path)
 
     # Retrieve information on package
     dsc_path = path.join(path.dirname(extracted_path), dsc_name)