heyvito/minicss: Ruby CSS parsing library

MiniCSS is a Ruby implementation of the CSS Syntax Level 3 tokenizer, parser, serializer, and selector toolkit. It provides fast, dependency-free primitives for building linters, minifiers, and other CSS-aware tooling. Features C tokenizer and parser for Ruby 3.4+. Battle-tested against the JSON-based css-parsing-tests suite for standards-compliant parsing. High-level AST wrappers (MiniCSS::AST::Rule, Decl, AtRule, Function, Number, and more) ready for programmatic inspection. Bidirectional selector helpers (MiniCSS::Sel) for tokenizing, walking, computing specificity, and turning selector ASTs back into strings. Serializer that converts AST nodes back into normalized CSS, enabling round-tripping and rewrites. Accepts either strings or IO objects, with optional Unicode range tokenization via allow_unicode_ranges.