Add a ListSyms type (vimwiki's g:vimwiki_listsyms) and thread it through
the lexer so checkbox glyphs are recognized from the configured palette
rather than the hardcoded ' .oOX'. Glyphs map to the existing five-bucket
CheckboxState, so the HTML renderer and AST consumers are unchanged.
VimwikiSyntax::parse_with_listsyms opts into a custom palette; the trait
parse() keeps the default.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
