🐛 fix: use timezone-aware datetimes in meetup schema

- Replace deprecated datetime.utcfromtimestamp() with datetime.fromtimestamp()
- Use pytz instead of Delorean for timezone conversion
- Fixes RuntimeWarning about naive datetimes in Python 3.13

Author: matrixise

pythonie/meetups/schema.py

@@ -1,12 +1,14 @@
-from datetime import datetime
+from datetime import datetime, timezone
 
 import colander
-from delorean import Delorean
+import pytz
 
 
 def int_to_datetime(value):
-    time = datetime.utcfromtimestamp(value / 1000)
-    return Delorean(time, timezone="UTC").shift("Europe/Dublin").datetime
+    """Convert Unix timestamp in milliseconds to timezone-aware datetime."""
+    utc_dt = datetime.fromtimestamp(value / 1000, tz=timezone.utc)
+    dublin_tz = pytz.timezone("Europe/Dublin")
+    return utc_dt.astimezone(dublin_tz)
 
 
 class Meetups(colander.MappingSchema):