chore: rename StartReturningModel to Run

Added aliases for the old functions, but deprecated them.

examples/composable-views/main.go

@@ -156,7 +156,7 @@ func (m *mainModel) resetSpinner() {
 func main() {
 	p := tea.NewProgram(newModel(defaultTime))
 
-	if err := p.Start(); err != nil {
+	if _, err := p.Run(); err != nil {
 		log.Fatal(err)
 	}
 }