Function parse_basic_subtitle 

pub fn parse_basic_subtitle(file_name: &str) -> SubtitleTitleInfo

Public entry: mirror C# LanguageParser.ParseBasicSubtitle (lines 252-260).

Composes parse_language_tags and parse_subtitle_language into a minimal SubtitleTitleInfo (only language_tags, language, and title_first = false are populated; raw_title/title/copy stay at defaults).