Refactor user ID handling to use UUIDs; update related components and serializers for consistency

backend/server/worldtravel/serializers.py

@@ -1,6 +1,8 @@
 import os
 from .models import Country, Region, VisitedRegion
 from rest_framework import serializers
+from main.utils import CustomModelSerializer
+
 
 class CountrySerializer(serializers.ModelSerializer):
     def get_public_url(self, obj):
@@ -36,7 +38,7 @@ class RegionSerializer(serializers.ModelSerializer):
         fields = '__all__'
         read_only_fields = ['id', 'name', 'country', 'longitude', 'latitude']
 
-class VisitedRegionSerializer(serializers.ModelSerializer):
+class VisitedRegionSerializer(CustomModelSerializer):
     longitude = serializers.DecimalField(source='region.longitude', max_digits=9, decimal_places=6, read_only=True)
     latitude = serializers.DecimalField(source='region.latitude', max_digits=9, decimal_places=6, read_only=True)
     name = serializers.CharField(source='region.name', read_only=True)