`@layer`s nested inside style rules are not merged

When nesting an @layer inside a style rule it's properly lifted but multiple layers with the same name are not merged — whether minified or not. This merging typically happens even when not minifying but I think it would be acceptable if, to fix it, minification was required:

Playground Link

Input:

.foo {
  @layer utilities {
    color: red;
  }
}

.baz {
  @layer components {
    color: red;
  }
}

.bar {
  @layer utilities {
    color: red;
  }
}

Expected:

@layer utilities {
  .foo, .bar {
    color: red;
  }
}

@layer components {
  .baz {
    color: red;
  }
}

Actual:

@layer utilities {
  .foo {
    color: red;
  }
}

@layer components {
  .baz {
    color: red;
  }
}

@layer utilities {
  .bar {
    color: red;
  }
}

Reproduce the behavior using the linked Playground or the CSS input in the issue, comparing minified and non-minified output. Trace the nested @layer lifting and merging path, then verify that repeated utilities layers are combined while the components layer remains separate and the expected output is produced.