add nth child pseudo class

[pauloamed]

most of LOCs are testing

[pauloamed]

@sleepy-monax I'll need ur eyes here, pls

[sleepy-monax]

defaulting it works on my machine with 20.1.8

[pauloamed]

before merging, after the final review, ill switch to defaulting. its quicker than trying to set up the correct version

[Louciole]

i agree with the concept, looks generally good

[Copilot]

Pull Request Overview

This PR adds support for nth-child CSS pseudo-class selectors, implementing the ability to select elements based on their position among siblings. The implementation includes parsing of "An+B" expressions (like 2n+1, odd, even) and matching logic for various nth-child variants.

• Implements CSS nth-child pseudo-class selector parsing and matching
• Adds comprehensive AnB expression parsing for formulaic element selection
• Extends DOM tree functionality to support filtered element indexing

Reviewed Changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
tests/css/selectors.xhtml	Comprehensive test cases for nth-child pseudo-class selectors
src/vaev-engine/style/tests/test-select-spec.cpp	Unit tests for AnB expression matching logic
src/vaev-engine/style/tests/test-parse-selectors.cpp	Parser tests for AnB expressions and nth-child selectors
src/vaev-engine/style/selector.cpp	Core implementation of AnB parsing and nth-child selector support
src/vaev-engine/style/selector-impl.cpp	Equality operator implementations for selector types
src/vaev-engine/style/matcher.cpp	Matching logic for nth-child pseudo-class selectors
src/vaev-engine/dom/tree.cpp	DOM tree index functions with filtering support

[sleepy-monax]

Great work as always