[CLI] Fix argument help rendering with click 8.5 (#4759)
click 8.5.0 gave `click.Argument` its own `help` parameter and added a
`format_arguments` step to `Command.format_help`. Both broke the CLI's
help rendering:
- `HfArgument.__init__` set `self.help` before calling `super().__init__()`,
so click's new constructor reset it to `None` and argument descriptions
disappeared from `--help` (and from the generated `cli.md`).
- Click's native "Positional arguments" section was printed on top of the
one `HfCommand.format_options` already renders.
The fix stays compatible with click 8.4, so no version cap or floor bump
is needed.
Co-authored-by: Claude Opus 5 (1M context) <noreply@anthropic.com>