Describe the feature

In a large project, it is difficult to track/manage when developers specify properties with a value that already exists in the default object. It would be nice to add a warning option if redundant duplication occurs:

const defuFn = createDefu({ 
  warnDuplicates: true
})

On the other hand, I guess it's better not to cause side effects, maybe a callback?

const defuFn = createDefu({ 
  onDuplicate: (object, key, value) => {}
})

Additional information

• Would you be willing to help implement this feature?