Use leak detection of DebugAllocator.

When allocating memory it remebers where memory was allocated but it only
for leaks in .deinit(). So not calling it is a sure way to miss a bunch of leaks.

deinit() returns if it found leaks but we don't really care. Its usefull for tests but not here.

src/main.zig

@@ -5,7 +5,9 @@ const WindowContext = @import("WindowContext.zig");
 const ui = @import("ui/frame.zig");
 
 pub fn main() !void {
-    var gpa = std.heap.GeneralPurposeAllocator(.{}){};
+    // std.heap.GeneralPurposeAllocator was renamed to DebugAllocator recently.
+    var gpa: std.heap.DebugAllocator(.{}) = .init;
+    defer _ = gpa.deinit();
     const allocator = gpa.allocator();
 
     var backend = try SDLBackend.initWindow(.{