- Replace map[string]interface{} with map[string]any in GraphQL, metrics, payment gateway, and webhook handlers
- Replace []byte(fmt.Sprintf()) with fmt.Appendf(nil, ...) for cursor encoding in GraphQL resolvers and tests
- Replace strings.HasPrefix/TrimPrefix with strings.CutPrefix for webhook signature parsing
- Replace stripe.Int64/Bool with new() constructor for Stripe payment parameters
- Rename Error
- Add TimeSeriesStorage with InfluxDB client, write API, and query API for org/bucket
- Add metric types: MetricPoint, UsageMetrics, SystemMetrics, ChargingMetrics with subscriber/IMSI/transaction fields
- Add StoreUsageMetrics, StoreSystemMetrics, StoreChargingMetrics, and StorePacketMetrics to write metrics to InfluxDB
- Add GetUsageStats to query subscriber usage statistics for time range with last aggreg