feature : validate tag

[panapol-p]

validate diff:id tag for create map key (diff:id is mandatory)

type FeedData struct {
	ID    string `diff:"id"`
	Name  string
	Score float32
}

[panapol-p]

idea of this issue

fs := []FeedData{
   {ID: "1", Name: "Bob", Score: 98.50},
   {ID: "2", Name: "Joe", Score: 92.50},
}
//return error after create new Diff
d,err  := diff.NewDiff[FeedData]()

if not found tag diff:id in struct then return error no tag