Fix __future__ imports, __metaclass__ = type, and remove explicit UTF-8 encoding statement for Python files (#10886)

* Adjust all __future__ imports:

for i in $(grep -REl "__future__.*absolute_import" plugins/ tests/); do
  sed -e 's/from __future__ import .*/from __future__ import annotations/g' -i $i;
done

* Remove all UTF-8 encoding specifications for Python source files:

for i in $(grep -REl '[-][*]- coding: utf-8 -[*]-' plugins/ tests/); do
  sed -e '/^# -\*- coding: utf-8 -\*-/d' -i $i;
done

* Remove __metaclass__ = type:

for i in $(grep -REl '__metaclass__ = type' plugins/ tests/); do
  sed -e '/^__metaclass__ = type/d' -i $i;
done

tests/unit/plugins/modules/test_xdg_mime.yaml

@@ -1,4 +1,3 @@
-# -*- coding: utf-8 -*-
 # Copyright (c) 2025, Marcos Alano <marcoshalano@gmail.com>
 # Based on gio_mime module. Copyright (c) 2022, Alexei Znamensky <russoz@gmail.com>
 # GNU General Public License v3.0+ (see LICENSES/GPL-3.0-or-later.txt or https://www.gnu.org/licenses/gpl-3.0.txt)