Use .iterator() idiom in init_tags

to avoid loading all events into memory before looping over them

There's some warnings in the docs about SQLite and iterators, but
I don't think those apply, for one because we don't write to the
events: https://docs.djangoproject.com/en/5.1/ref/databases/#sqlite-isolation

tags/management/commands/init_tags.py

@@ -19,7 +19,7 @@ class Command(BaseCommand):
         t0 = time.time()
 
         try:
-            for i, event in enumerate(Event.objects.all()):
+            for i, event in enumerate(Event.objects.all().iterator()):
                 # transaction per event: allows for interrupting the process without losing all progress; also allows
                 # for your server to remain responsive during the process
                 with immediate_atomic():