feat: enhance observability with prefix aggregation metrics

- Added new histograms to track prefix aggregation duration, raw count, and aggregated count during tenant rendering.
- Implemented `RecordPrefixAggregation` function to record metrics for aggregation performance.
- Updated `RenderTenantRevision` and `RenderTenantRevisionFromPrefixes` functions to log aggregation statistics.
- Refactored `smartAggregatePrefixRows` to support both IPv4 and IPv6 aggregation, improving overall prefix handling.

internal/observability/metrics.go

@@ -59,8 +59,42 @@ var (
 		Name:      "build_info",
 		Help:      "Build metadata (value always 1).",
 	}, []string{"version", "git_sha"})
+
+	prefixAggregationDuration = promauto.NewHistogram(prometheus.HistogramOpts{
+		Namespace: namespace,
+		Name:      "prefix_aggregation_duration_seconds",
+		Help:      "Time spent in smartAggregatePrefixRows during tenant render.",
+		Buckets:   prometheus.ExponentialBuckets(0.0001, 2, 16),
+	})
+
+	prefixAggregationRawCount = promauto.NewHistogram(prometheus.HistogramOpts{
+		Namespace: namespace,
+		Name:      "prefix_aggregation_raw_count",
+		Help:      "Prefix row count before CIDR aggregation on tenant render.",
+		Buckets:   prometheus.ExponentialBuckets(1, 2, 16),
+	})
+
+	prefixAggregationAggregatedCount = promauto.NewHistogram(prometheus.HistogramOpts{
+		Namespace: namespace,
+		Name:      "prefix_aggregation_aggregated_count",
+		Help:      "Prefix row count after CIDR aggregation on tenant render.",
+		Buckets:   prometheus.ExponentialBuckets(1, 2, 16),
+	})
 )
 
+// RecordPrefixAggregation records tenant render CIDR aggregation stats.
+func RecordPrefixAggregation(rawCount, aggregatedCount int, duration time.Duration) {
+	if rawCount < 0 {
+		rawCount = 0
+	}
+	if aggregatedCount < 0 {
+		aggregatedCount = 0
+	}
+	prefixAggregationDuration.Observe(duration.Seconds())
+	prefixAggregationRawCount.Observe(float64(rawCount))
+	prefixAggregationAggregatedCount.Observe(float64(aggregatedCount))
+}
+
 // RecordJobTerminal increments jobs_finished_total for terminal statuses.
 func RecordJobTerminal(kind, status string) {
 	switch status {