Fix plugin

[ScarletEmanu]

• This fix issue: Problem with plugin #3021

PR Description:

Changes in archinstall/lib/args.py:

• Arguments: added plugin_url: str | None and changed plugin to Path | None for consistency with creds.
• CLI: --plugin now uses type=Path (was str); added a new --plugin-url option to specify a remote plugin location.
• _parse_args: if --plugin is set, loads the plugin from the local path as before. If --plugin-url is set instead, the content is downloaded via the existing _fetch_from_url helper and written to a local temp file via a new _write_plugin_to_temp_file helper, then that local path is passed to load_plugin.

Changes in archinstall/lib/plugins.py:

• Removed _localize_path and the URL-handling branch in load_plugin and now-unused imports (hashlib, urllib.parse, urllib.request).

Tests and Checks

• [x ] I have tested the code!

[ScarletEmanu]

@svartkanin @codefiles @Torxed anyone of you can review this please. Thanks

[Torxed]

Nice cleanup!