fix(ratchet): refuse a package directory that does not exist

napalm-hpe-aruba-procurve ships napalm_procurve; guessed from its name, the
ratchet measured nothing and wrote an empty baseline without a word.

tests/test_cli.py

@@ -135,3 +135,12 @@ def test_package_prints_the_import_package(
 ) -> None:
     assert cli.main(["package", str(make_repo())]) == 0
     assert capsys.readouterr().out == "napalm_example\n"
+
+
+def test_ratchet_names_the_missing_package(
+    make_repo: RepoFactory, capsys: pytest.CaptureFixture[str]
+) -> None:
+    repo = make_repo({"napalm_example/__init__.py": None, "napalm_example/py.typed": None})
+
+    assert cli.main(["ratchet", "--write", str(repo)]) == 2
+    assert "[tool.napalm-standard] package" in capsys.readouterr().err