Closes #20516: Add ranges_to_string_list and render VLAN Group VID ranges with ArrayColumn

[pheus]

Fixes: #20516

Summary

• Add ranges_to_string_list(ranges) -> list[str], which formats numeric ranges as human‑readable strings (e.g., ["1-5", "8", "10-12"]).
• Refactor ranges_to_string(ranges) to delegate to the new helper:

  if not ranges:
      return ''
  return ','.join(ranges_to_string_list(ranges))

  This preserves the existing output (comma‑separated with no spaces) while enabling callers to control separators when needed.
• Improve VLAN Group rendering by switching the table column to use a list accessor with ArrayColumn, yielding ", " spacing in the UI without changing underlying data or the string helper’s behavior.

Implementation notes

• ranges_to_string remains fully backward‑compatible in both signature and output.
• VLAN Group table uses a list accessor (e.g., vid_ranges_items) with ArrayColumn, while keeping the existing vid_ranges_list string property available to avoid breaking saved table configs.

Testing

• Add unit tests covering:
  • Singleton ranges ("8") vs. hyphen ranges ("1-5")
  • ranges_to_string_list()

Backwards compatibility

• No breaking changes. Existing uses of ranges_to_string() and VLANGroup.vid_ranges_list continue to work as before.