fix: only add to history of different

if the last item in history is the same as the one being added, skip it.
this reduces the number of history entries. the behaviour is similar to
how most shells maintain history

readline/history.go

@@ -81,11 +81,13 @@ func (h *History) Init() error {
 }
 
 func (h *History) Add(s string) {
-	h.Buf.Add(s)
-	h.Compact()
-	h.Pos = h.Size()
-	if h.Autosave {
-		_ = h.Save()
+	if latest, _ := h.Buf.Get(h.Size() - 1); latest != s {
+		h.Buf.Add(s)
+		h.Compact()
+		h.Pos = h.Size()
+		if h.Autosave {
+			_ = h.Save()
+		}
 	}
 }