Show route churn as a whole count per minute (closes #160)

The status page showed route churn per second as a one-minute moving
average, so a quiet feed gave a fraction such as 0.1. The average was
correct.

The metrics tracker now also counts prefix announcements and
withdrawals, from all peers, in each clock minute. /api/v1/stats
reports the count for the last full minute as route_churn_per_min in
stream, in place of route_churn_per_sec. The status page shows it as
"Route Churn/min".

The status and home pages round messages and updates per second to
whole numbers.

Model: opus-5-5

internal/server/handlers_internal_test.go

@@ -195,6 +195,51 @@ func TestStatsHandlersAnswerFromMemory(t *testing.T) {
 	}
 }
 
+// TestStatsAnswerCarriesChurnPerMinute checks that the stream object of the
+// /api/v1/stats answer holds route_churn_per_min as a whole number, and no
+// longer route_churn_per_sec, the moving average it replaces
+// (https://git.eeqj.de/sneak/routewatch/issues/160).
+func TestStatsAnswerCarriesChurnPerMinute(t *testing.T) {
+	t.Parallel()
+
+	s := newServerWithTestRoutes(t)
+
+	rec := httptest.NewRecorder()
+	s.handleStats()(rec,
+		httptest.NewRequestWithContext(t.Context(), http.MethodGet, statsPath, nil))
+
+	if rec.Code != http.StatusOK {
+		t.Fatalf("status %d, want %d; body %s", rec.Code, http.StatusOK, rec.Body)
+	}
+
+	var body struct {
+		Data struct {
+			Stream map[string]json.RawMessage `json:"stream"`
+		} `json:"data"`
+	}
+
+	err := json.Unmarshal(rec.Body.Bytes(), &body)
+	if err != nil {
+		t.Fatalf("decoding the answer: %v", err)
+	}
+
+	churn, ok := body.Data.Stream["route_churn_per_min"]
+	if !ok {
+		t.Fatalf("stream has no route_churn_per_min: %s", rec.Body)
+	}
+
+	var count int
+
+	err = json.Unmarshal(churn, &count)
+	if err != nil {
+		t.Errorf("route_churn_per_min = %s, want a whole number: %v", churn, err)
+	}
+
+	if _, ok := body.Data.Stream["route_churn_per_sec"]; ok {
+		t.Errorf("stream still has route_churn_per_sec: %s", rec.Body)
+	}
+}
+
 // newServerWithTestRoutes returns a server on a new database that holds a
 // route for testPrefixV4 and one for testPrefixV6.
 func newServerWithTestRoutes(t *testing.T) *Server {