memory leak in example todo_list

[dacec354]

run zig build run-todo_list. Add a item and then quit to reproduce.

~/project/zig/zigzag> zig build run-todo_list
error(gpa): memory address 0x724a93720000 leaked:
/home/ett/.local/share/mise/installs/zig/0.15.2/lib/std/mem/Allocator.zig:436:40: 0x108104e in dupe__anon_5555 (std.zig)
    const new_buf = try allocator.alloc(T, m.len);
                                       ^
/home/ett/project/zig/zigzag/examples/todo_list.zig:54:76: 0x118a9a2 in update (todo_list.zig)
                                const title = ctx.persistent_allocator.dupe(u8, self.input.getValue()) catch return .none;
                                                                           ^
/home/ett/project/zig/zigzag/src/core/program.zig:282:37: 0x115e917 in dispatchToModel (root.zig)
            return self.model.update(user_msg, &self.context);
                                    ^
/home/ett/project/zig/zigzag/src/core/program.zig:321:44: 0x1162775 in processKeyEvent (root.zig)
                return self.dispatchToModel(user_msg);
                                           ^
/home/ett/project/zig/zigzag/src/core/program.zig:229:57: 0x1158a3d in tick (root.zig)
                        .key => |k| self.processKeyEvent(k),
                                                        ^
/home/ett/project/zig/zigzag/src/core/program.zig:120:30: 0x11596c7 in run (root.zig)
                try self.tick();