feat: upgrade gulp-sass from 5 to 6, refactoring, remove old @import syntax

Author: tedw

package.json

@@ -47,14 +47,14 @@
     "gulp-header": "^2.0.9",
     "gulp-load-plugins": "^2.0.8",
     "gulp-replace": "^1.1.4",
-    "gulp-sass": "^5.1.0",
+    "gulp-sass": "^6.0.1",
     "js-yaml": "^4.1.0",
     "postcss-scss": "^4.0.9",
     "sass": "^1.77.8",
     "sass-true": "^8.0.0",
     "sassdoc": "^2.7.4",
     "stylelint": "^16.8.2",
-    "stylelint-config-standard": "^36.0.1",
+    "stylelint-config-standard": "^38.0.0",
     "stylelint-scss": "^6.5.0"
   }
 }

tests/functions/_easings.scss

@@ -1,3 +1,11 @@
+// Sass unit testing using Oddbird
+// https://www.oddbird.net/true/docs/
+// https://github.com/oddbird/true
+@use '../node_modules/sass-true' as *;
+
+// Import Frontline
+@use '../src/_frontline' as *;
+
 @include test-module('Easing helper [function]') {
   @include test('Returns custom cubic-bezier() easing function') {
     // Assert the expected results

tests/functions/_index.scss

@@ -1,2 +1 @@
-@import "easings";
-// @import "scale-clamp";
+@forward "easings";

tests/mixins/_absolute-fill.scss

@@ -1,3 +1,11 @@
+// Sass unit testing using Oddbird
+// https://www.oddbird.net/true/docs/
+// https://github.com/oddbird/true
+@use '../node_modules/sass-true' as *;
+
+// Import Frontline
+@use '../src/_frontline' as *;
+
 @include it('Absolutely position an element and fill available space') {
   @include assert {
     @include output {

tests/mixins/_index.scss

@@ -1 +1 @@
-@import "absolute-fill";
+@forward "absolute-fill";

tests/tests.scss

@@ -1,11 +1,3 @@
-// Sass unit testing using Oddbird
-// https://www.oddbird.net/true/docs/
-// https://github.com/oddbird/true
-@import '../node_modules/sass-true/sass/true';
-
-// Import Frontline
-@import '../src/_frontline';
-
 // Tests
-@import "functions/index";
-@import "mixins";
+@use "functions/index" as *;
+@use "mixins/index" as *;