Add MetaOCaml support Add a --metaocaml flag to enable MetaOCaml syntax (brackets .< >., escape .~, run .!) in the lexer and formatter. Lexer changes: - Split symbolchar into symbolcharnodot/symbolchar to avoid capturing MetaOCaml tokens as operator characters - Gate .~ (escape) and >. (bracket close) behind the metaocaml flag; .< (bracket open) is always lexed as METAOCAML_BRACKET_OPEN - Add symbolchars sub-lexer for consuming remaining operator chars after >. when metaocaml is disabled - Thread ~metaocaml through parse.ml to set lex_metaocaml ref Formatter changes: - Detect metaocaml.bracket and metaocaml.escape extension nodes (synthetic, with ghost loc) and render them with sugar syntax (.< expr >. and .~expr) instead of [%metaocaml.bracket ...] - Parenthesize .~ argument unless it is a simple identifier - Skip comment relocation for metaocaml extension nodes in Cmts Configuration: - Add metaocaml boolean to opr_opts (Conf_t), default false - Wire --metaocaml/--no-metaocaml flag through Conf and CLI - Thread ~metaocaml through Extended_ast, Std_ast, Parse_with_comments, Toplevel_lexer