Pause spinner ticks when not refreshing.

Also, add a quick-and-dirty model for displaying basic performance
stats, currently just the number of calls to the root Update() and
View() methods.

tui/asset/asset.go

@@ -108,11 +108,16 @@ func (m Model) Update(msg tea.Msg) (Model, tea.Cmd) {
 		switch msg := msg.inner.(type) {
 		case refresh:
 			m.refreshing = true
-			return m, func() tea.Msg {
-				// TODO: log errors
-				_ = m.math.Refresh(context.TODO())
-				return Msg{m.math.Asset, m.math}
-			}
+			return m, tea.Batch(
+				func() tea.Msg {
+					return m.indicator.Tick()
+				},
+				func() tea.Msg {
+					// TODO: log errors
+					_ = m.math.Refresh(context.TODO())
+					return Msg{m.math.Asset, m.math}
+				},
+			)
 		case moon.Math:
 			m.math = msg
 			refillProperties(&m)
@@ -135,6 +140,9 @@ func (m Model) Update(msg tea.Msg) (Model, tea.Cmd) {
 			return m, nil
 		}
 	case spinner.TickMsg:
+		if !m.refreshing {
+			return m, nil
+		}
 		var cmd tea.Cmd
 		m.indicator, cmd = m.indicator.Update(msg)
 		return m, cmd