Replace timer-based SMA with a timer-less implementation

time/source.go

@@ -0,0 +1,25 @@
+package time
+
+import "time"
+
+type Source interface {
+	Now() time.Time
+}
+
+type StdSource struct{}
+
+func (s *StdSource) Now() time.Time {
+	return time.Now()
+}
+
+type TestSource struct {
+	N time.Time
+}
+
+func (t *TestSource) Now() time.Time {
+	return t.N
+}
+
+func (t *TestSource) Set(sec int64, nsec int64) {
+	t.N = time.Unix(sec, nsec)
+}