fix(go): cache mileage after successful write

go/vehicle-gateway/internal/stats/daily_metric.go

@@ -65,6 +65,7 @@ func (w *Writer) Append(ctx context.Context, env envelope.FrameEnvelope) error {
 			sample.TotalMileageKM); err != nil {
 			return err
 		}
+		w.markMileageWritten(sample)
 	}
 	return nil
 }
@@ -77,13 +78,20 @@ func (w *Writer) seenSameMileage(sample MetricSample) bool {
 	if last, ok := w.lastTotalMileage[key]; ok && last == sample.TotalMileageKM {
 		return true
 	}
+	return false
+}
+
+func (w *Writer) markMileageWritten(sample MetricSample) {
+	prefix := fmt.Sprintf("%s|%s|", sample.VIN, sample.Protocol)
+	key := prefix + sample.StatDate
+	w.mu.Lock()
+	defer w.mu.Unlock()
 	for existing := range w.lastTotalMileage {
 		if strings.HasPrefix(existing, prefix) && existing != key {
 			delete(w.lastTotalMileage, existing)
 		}
 	}
 	w.lastTotalMileage[key] = sample.TotalMileageKM
-	return false
 }
 
 func SamplesFromEnvelope(env envelope.FrameEnvelope, loc *time.Location) ([]MetricSample, error) {