style: autoformat src and tests

Repository-wide formatting pass over src/ and tests/: sorted imports and
__all__ entries, dropped redundant `# -*- coding: utf-8 -*-` headers,
unquoted forward-reference annotations (safe under
`from __future__ import annotations`), merged nested `with` statements,
moved `Iterable` and friends from `typing` to `collections.abc`, and
removed `# noqa: F401` markers that no longer suppress anything.

No behavioural changes. Unit and integration suites show the same four
pre-existing failures before and after the pass.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

tests/e2e/test_release_commands.py

@@ -1,5 +1,4 @@
 #!/usr/bin/env python3
-# -*- coding: utf-8 -*-
 
 """
 End-to-end style integration tests for the `pkgmgr release` CLI command.
@@ -141,8 +140,8 @@ class TestIntegrationReleaseCommand(unittest.TestCase):
         This test intentionally does not mock anything to exercise the real
         CLI parser wiring in main.py.
         """
-        import io
         import contextlib
+        import io
 
         original_argv = list(sys.argv)
         buf = io.StringIO()