Major schema refactoring: simplify ASN and prefix tracking

- Remove UUID primary keys from ASNs table, use ASN number as primary key
- Update announcements table to reference ASN numbers directly
- Rename asns.number column to asns.asn for consistency
- Add prefix tracking to PrefixHandler to populate prefixes_v4/v6 tables
- Add UpdatePrefixesBatch method for efficient batch updates
- Update all database methods and models to use new schema
- Fix all references in code to use ASN field instead of Number
- Update test mocks to match new interfaces

internal/database/interface.go

@@ -27,6 +27,7 @@ type Store interface {
 
 	// Prefix operations
 	GetOrCreatePrefix(prefix string, timestamp time.Time) (*Prefix, error)
+	UpdatePrefixesBatch(prefixes map[string]time.Time) error
 
 	// Announcement operations
 	RecordAnnouncement(announcement *Announcement) error