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/integration/test_recursive_capabilities.py

@@ -1,5 +1,4 @@
 #!/usr/bin/env python3
-# -*- coding: utf-8 -*-
 
 """
 Integration tests for recursive capability resolution and installer shadowing.
@@ -17,7 +16,8 @@ import os
 import shutil
 import tempfile
 import unittest
-from typing import List, Sequence, Tuple
+from collections.abc import Sequence
+from typing import List, Tuple
 from unittest.mock import patch
 
 import pkgmgr.actions.install as install_mod
@@ -29,7 +29,6 @@ from pkgmgr.actions.install.installers.os_packages.arch_pkgbuild import (
 )
 from pkgmgr.actions.install.installers.python import PythonInstaller
 
-
 InstallerSpec = Tuple[str, object]