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/store/memory.go

@@ -327,13 +327,22 @@ func (m *Memory) CreateRenderRevision(revisionID, tenantID, moduleID string, par
 		frag[k] = v
 	}
 	parent := parentRevisionID
+	createdAt := time.Now().UTC()
+	for _, r := range m.revisions {
+		if r == nil || r.TenantID != tenantID {
+			continue
+		}
+		if !r.CreatedAt.Before(createdAt) {
+			createdAt = r.CreatedAt.Add(time.Microsecond)
+		}
+	}
 	m.revisions[revisionID] = &Revision{
 		ID:                      revisionID,
 		TenantID:                tenantID,
 		ModuleID:                moduleID,
 		ContentHash:             contentHash,
 		ParentRevisionID:        parent,
-		CreatedAt:               time.Now().UTC(),
+		CreatedAt:               createdAt,
 		MaterializedPrefixCount: len(prefixes),
 		PreviewFragments:        frag,
 	}
@@ -657,6 +666,9 @@ func (m *Memory) ListRevisions(tenantID, moduleID string, cursor string, limit i
 		all = append(all, r)
 	}
 	sort.Slice(all, func(i, j int) bool {
+		if all[i].CreatedAt.Equal(all[j].CreatedAt) {
+			return all[i].ID > all[j].ID
+		}
 		return all[i].CreatedAt.After(all[j].CreatedAt)
 	})
 	off := 0