test ✅: add coverage for shared utility functions

Add comprehensive tests for shared utility modules to improve code coverage:

- Test property name extraction edge cases
- Test CSS property priority map with invalid groups
- Test order strategy visitor creator edge cases
- Test font face property order enforcer early returns
- Test style node processor with arrays and null values

These tests ensure all code paths in shared utilities are properly exercised,
including error handling and edge cases.

src/css-rules/shared-utils/__tests__/property-name-extractor.test.ts

@@ -0,0 +1,57 @@
+import tsParser from '@typescript-eslint/parser';
+import { run } from 'eslint-vitest-rule-tester';
+import testRuleForPropertyNameExtractor from './test-property-name-rule.js';
+
+run({
+  name: 'vanilla-extract/property-name-extractor-tests',
+  rule: testRuleForPropertyNameExtractor,
+  languageOptions: {
+    parser: tsParser,
+    parserOptions: {
+      ecmaVersion: 2022,
+      sourceType: 'module',
+    },
+  },
+  valid: [
+    // Test for identifier and string literal keys (should return names)
+    `
+      import { style } from '@vanilla-extract/css';
+
+      const myStyle = style({
+        color: 'blue',
+        'background-color': 'white',
+        fontSize: '16px'
+      });
+    `,
+
+    // Test for computed property with non-string literal (should return empty string)
+    `
+      import { style } from '@vanilla-extract/css';
+
+      const myStyle = style({
+        [42]: 'numeric key',
+        [true]: 'boolean key'
+      });
+    `,
+
+    // Test for computed property with complex expression
+    `
+      import { style } from '@vanilla-extract/css';
+
+      const myStyle = style({
+        [Math.random() > 0.5 ? 'dynamicKey' : 'otherKey']: 'dynamic value'
+      });
+    `,
+
+    // Test for property with template literal key
+    `
+      import { style } from '@vanilla-extract/css';
+
+      const prefix = 'webkit';
+      const myStyle = style({
+        [\`-\${prefix}-appearance\`]: 'none'
+      });
+    `,
+  ],
+  invalid: [],
+});