`@import` layer information missing in dependencies when `analyzeDependencies` is enabled

[aneuhold]

When analyzeDependencies: true is enabled, the layer field from @import rules is not included in the dependency metadata. The url and media fields are preserved correctly.

Reproduction

Repository: https://github.com/aneuhold/lightningcss-layer-bug

import { transform } from 'lightningcss';

const css = `@import url('test.css') layer(external) not print;`;
const result = transform({
  filename: 'test.css',
  code: Buffer.from(css),
  analyzeDependencies: true,
});

console.log(result.dependencies[0]);
// {
//   type: 'import',
//   url: 'test.css',
//   media: 'not print',  // ✅ preserved
//   // layer field is missing
// }

Expected

The dependency object should include a layer field:

{
  type: 'import',
  url: 'test.css',
  layer: 'external',
  media: 'not print'
}

Test Results

All layer variants are missing:

Input	Expected layer	Actual
@import url('x') layer(external);	'external'	Missing
@import url('x') layer;	null or true	Missing
@import url('x') layer(base) screen;	'base'	Missing

Context

• Lightning CSS npm v1.30.2 (Rust crate v1.0.0-alpha.68)
• The ImportRule struct in src/rules/import.rs has a layer field
• The ImportDependency::new() method in src/dependencies.rs extracts supports and media but not layer

This affects bundlers (including Turbopack) that rely on dependency metadata to reconstruct CSS imports with proper cascade layer ordering per the CSS Cascade 5 spec.