geometry: make Rectangle.grow and Rectangle.shrink return a new one

src/geometry.zig

@@ -100,19 +100,23 @@ pub fn Rectangle(comptime T: type) type {
         }
 
         /// Grows the given rectangle by expaning its borders by `amount`.
-        pub fn grow(self: *Self, amount: T) void {
-            self.l -|= amount;
-            self.t -|= amount;
-            self.r += amount;
-            self.b += amount;
+        pub fn grow(self: Self, amount: T) Self {
+            return .{
+                .l = self.l -| amount,
+                .t = self.t -| amount,
+                .r = self.r + amount,
+                .b = self.b + amount,
+            };
         }
 
         /// Shrinks the given rectangle by shrinking its borders by `amount`.
-        pub fn shrink(self: *Self, amount: T) void {
-            self.l += amount;
-            self.t += amount;
-            self.r -|= amount;
-            self.b -|= amount;
+        pub fn shrink(self: Self, amount: T) Self {
+            return .{
+                .l = self.l + amount,
+                .t = self.t + amount,
+                .r = self.r -| amount,
+                .b = self.b -| amount,
+            };
         }
     };
 }
@@ -131,13 +135,12 @@ test "Rectangle" {
 
 test "Rectangle grow and shrink" {
     const rect = Rectangle(i32){ .l = 50, .t = 25, .r = 100, .b = 100 };
-    var rect2 = rect;
     const amount: i32 = 10;
-    rect2.grow(amount);
+    var rect2 = rect.grow(amount);
     try expectEqual(rect.width() + 2 * amount, rect2.width());
     try expectEqual(rect.height() + 2 * amount, rect2.height());
     try expectEqualDeep(rect2, Rectangle(i32){ .l = 40, .t = 15, .r = 110, .b = 110 });
-    rect2.shrink(10);
+    rect2 = rect2.shrink(10);
     try expectEqualDeep(rect, rect2);
 }