Refactor database handlers and optimize PeeringHandler

- Create PeeringHandler for asn_peerings table maintenance
- Rename DBHandler to ASHandler (now only handles asns table)
- Move prefixes table maintenance to PrefixHandler
- Optimize PeeringHandler with in-memory AS path tracking:
  - Stores AS paths in memory with timestamps
  - Processes peerings in batch every 2 minutes
  - Prunes old paths (>30 minutes) every 5 minutes
  - Normalizes peerings with lower AS number first
- Each handler now has a single responsibility:
  - ASHandler: asns table
  - PeerHandler: bgp_peers table
  - PrefixHandler: prefixes and live_routes tables
  - PeeringHandler: asn_peerings table

internal/routewatch/app_integration_test.go

@@ -224,6 +224,11 @@ func TestRouteWatchLiveFeed(t *testing.T) {
 	// Wait for the configured duration
 	time.Sleep(5 * time.Second)
 
+	// Force peering processing for test
+	if rw.peeringHandler != nil {
+		rw.peeringHandler.ProcessPeeringsNow()
+	}
+
 	// Get statistics
 	stats, err := mockDB.GetStats()
 	if err != nil {