refactor(db): normalize asn prefix cache and ttl cleanup

Строки asn_prefix_cache_row; периодический prune через evobgp-ingest.

Co-authored-by: Cursor <[email protected]>

internal/store/backend.go

@@ -112,6 +112,9 @@ type Backend interface {
 
 	// Ping verifies backend connectivity (no-op for in-memory).
 	Ping(ctx context.Context) error
+
+	// RunPeriodicMaintenance prunes stale DB rows (no-op for in-memory).
+	RunPeriodicMaintenance(ctx context.Context)
 }
 
 // ASNPrefixCacheEntry is a cached RIPEstat response for one ASN.