Improve nine-slice atlas sampling

test/runtime/rendering/runtime_component_test.dart

@@ -284,6 +284,36 @@ void main() {
       expect(parts[4].source, const Rect.fromLTRB(10, 10, 20, 20));
     });
 
+    test('insets nine-slice source rects to avoid atlas edge sampling', () {
+      final parts = runtimeNineSliceRects(
+        source: const Rect.fromLTWH(10, 20, 30, 30),
+        destination: const Rect.fromLTWH(0, 0, 90, 90),
+        sliceLeft: 10,
+        sliceTop: 10,
+        sliceRight: 10,
+        sliceBottom: 10,
+        sourceInset: 0.5,
+      );
+
+      expect(parts.first.source, const Rect.fromLTRB(10.5, 20.5, 19.5, 29.5));
+      expect(parts[4].source, const Rect.fromLTRB(20.5, 30.5, 29.5, 39.5));
+      expect(parts.last.source, const Rect.fromLTRB(30.5, 40.5, 39.5, 49.5));
+    });
+
+    test('keeps tiny nine-slice source rects when inset would collapse them', () {
+      final parts = runtimeNineSliceRects(
+        source: const Rect.fromLTWH(0, 0, 3, 3),
+        destination: const Rect.fromLTWH(0, 0, 30, 30),
+        sliceLeft: 1,
+        sliceTop: 1,
+        sliceRight: 1,
+        sliceBottom: 1,
+        sourceInset: 0.5,
+      );
+
+      expect(parts[4].source, const Rect.fromLTRB(1, 1, 2, 2));
+    });
+
     test('updates text alpha style without rebuilding text component', () {
       final component = RuntimeComponent(
         node: const RuntimeNode(