Optimize database batch operations with prepared statements

- Add prepared statements to all batch operations for better performance
- Fix database lock contention by properly batching operations
- Update SQLite settings for extreme performance (8GB cache, sync OFF)
- Add proper error handling for statement closing
- Update tests to properly track batch operations

internal/routewatch/ashandler.go

@@ -144,11 +144,9 @@ func (h *ASHandler) flushBatchLocked() {
 		}
 	}
 
-	for asn, ts := range asnMap {
-		_, err := h.db.GetOrCreateASN(asn, ts)
-		if err != nil {
-			h.logger.Error("Failed to get/create ASN", "asn", asn, "error", err)
-		}
+	// Process all ASNs in a single batch transaction
+	if err := h.db.GetOrCreateASNBatch(asnMap); err != nil {
+		h.logger.Error("Failed to process ASN batch", "error", err, "count", len(asnMap))
 	}
 
 	// Clear batch