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-vim.vim

@@ -651,6 +651,24 @@ call s:record(
       \ 'cmd.VimwikiTable_accepts_cols_rows',
       \ 'err=' . s:tbl_err)
 
+" ===== :VimwikiListChangeLvl -range -nargs=+ =====
+" Was -nargs=? (range-less): `:1,3VimwikiListChangeLvl increase 0` raised E481
+" (no range allowed) and/or E488 (trailing chars). The level change is an LSP
+" roundtrip (no server here), so assert only the attribute parse: no E481/E488.
+call s:set_buf(['- a', '- b', '- c'])
+let s:lcl_err = ''
+try
+  silent 1,3VimwikiListChangeLvl increase 0
+catch /E481\|E488/
+  let s:lcl_err = v:exception
+catch
+  " non-attribute error (e.g. no LSP) is expected and fine here.
+endtry
+call s:record(
+      \ s:lcl_err ==# '' ? 1 : 0,
+      \ 'cmd.VimwikiListChangeLvl_accepts_range_and_args',
+      \ 'err=' . s:lcl_err)
+
 " ===== Wrap up =====
 
 call add(s:results, '')