feat(commands): VimwikiListChangeLvl -range -nargs=+ (P3 parity)

Upstream is `-range -nargs=+` (change_level(line1, line2, direction,
plus_children)); nuwiki was -nargs=? and range-less, so `:1,3VimwikiListChangeLvl
increase 0` raised E481/E488 and the level change never spanned a selection.

All four defs (Vim+Neovim × Vimwiki+Nuwiki) are now -range -nargs=+ and forward
<line1>, <line2>, <f-args>. list_change_lvl(line1, line2, direction,
[plus_children]) (both clients) parses the required direction + optional subtree
flag and applies the change to every list item in the range via the existing
over_range helper.

Tests: cmd.ListChangeLvl_range_indents (test-keymaps.lua) +
cmd.VimwikiListChangeLvl_accepts_range_and_args (test-keymaps-vim.vim).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

development/tests/test-keymaps.lua

@@ -834,6 +834,21 @@ vim.defer_fn(function()
       error('want 5 table lines (hdr+sep+3 rows), got ' .. #tbl)
     end
   end)
+  -- `:[range]VimwikiListChangeLvl {dir} [plus_children]` — now -range -nargs=+
+  -- (was -nargs=?, range-less). A 1,3 range with `increase` must indent the
+  -- items that have somewhere to nest (the 2nd item under the 1st).
+  tobj_case('cmd.ListChangeLvl_range_indents', function()
+    set_buf({ '- a', '- b', '- c' })
+    vim.cmd('1,3VimwikiListChangeLvl increase 0')
+    local done = vim.wait(2000, function()
+      local l = vim.api.nvim_buf_get_lines(0, 0, -1, false)
+      return l[2] ~= nil and l[2]:match('^%s%s*%-') ~= nil
+    end, 30)
+    if not done then
+      error('range list-change-lvl did not indent: '
+        .. vim.inspect(vim.api.nvim_buf_get_lines(0, 0, -1, false)))
+    end
+  end)
   -- `:VimwikiNormalizeLink 1` (the arg is upstream's visual flag; the command
   -- is -nargs=? not -range, so no `'<,'>`) wraps the last visual selection.
   tobj_case('cmd.normalize_link_visual_wraps_selection', function()