fix(gateway): recover bounded pacing debt

gateway/telemetry.go

@@ -126,6 +126,7 @@ type fairPacer struct {
 type fairPacerFlow struct {
 	next     time.Time
 	lastSeen time.Time
+	debt     time.Duration
 }
 
 const fairPacerMaximumCatchup = 5 * time.Millisecond
@@ -180,9 +181,14 @@ func (p *fairPacer) reserveAt(now time.Time, flow string, bytes int) time.Time {
 		base = now
 	} else if lag := now.Sub(base); lag > fairPacerMaximumCatchup {
 		base = now.Add(-fairPacerMaximumCatchup)
+		state.debt = min(state.debt+lag-fairPacerMaximumCatchup, nativeApolloVideoQueueLatency-fairPacerMaximumCatchup)
 	}
 	numerator := int64(bytes) * int64(len(p.flows)) * int64(time.Second)
 	delay := time.Duration((numerator + p.bytesPerSecond - 1) / p.bytesPerSecond)
+	if repayment := min(delay/21, state.debt); repayment > 0 {
+		delay -= repayment
+		state.debt -= repayment
+	}
 	state.next = base.Add(delay)
 	p.flows[flow] = state
 	return state.next