Step 3a: CSS tokenizer — CSS Syntax Level 3

[thomasnemer]

Parent: #22

Goal

Implement the CSS tokenizer per CSS Syntax Module Level 3. Iterator-based, yields CssToken values.

File Changes

• crates/ie-css/src/tokenizer.rs — new file
• crates/ie-css/src/lib.rs — update modules
• crates/ie-css/Cargo.toml — if needed

Implementation

• CssToken enum: Ident, Function, AtKeyword, Hash, String, Url, Delim, Number, Percentage, Dimension, Whitespace, Colon, Semicolon, Comma, brackets, Cdo, Cdc, Eof
• Handle escape sequences, string tokens, URL tokens, comments
• Numbers: integer vs number distinction
• Iterator-based

Tests

• Simple rule tokens, strings with escapes, URL tokens, dimensions, percentages, functions
• ~10 unit tests

Acceptance Criteria

• cargo test -p ie-css passes
• Clippy clean