mod(memory): do not create items on the stack instead using the provided allocator

src/widget/Spacer.zig

@@ -11,15 +11,19 @@ pub fn Widget(comptime Event: type, comptime Renderer: type) type {
         @compileError("Provided user event `Event` for `Layout(comptime Event: type)` is not of type `union(enum)`.");
     }
     return struct {
-        size: terminal.Size = undefined,
-        size_changed: bool = false,
+        allocator: std.mem.Allocator,
+        size: terminal.Size,
+        size_changed: bool,
 
-        pub fn init() @This() {
-            return .{};
+        pub fn init(allocator: std.mem.Allocator) *@This() {
+            var this = allocator.create(@This()) catch @panic("Space.zig: Failed to create.");
+            this.allocator = allocator;
+            this.size_changed = true;
+            return this;
         }
 
         pub fn deinit(this: *@This()) void {
-            this.* = undefined;
+            this.allocator.destroy(this);
         }
 
         pub fn handle(this: *@This(), event: Event) ?Event {