Use aware objects when storing and reading UTC timestamps (#4017)

* Use aware objects instead of naive ones

* Use aware objects when storing and reading UTC timestamps

* Remove unneeded parentheses

* Fixed naive and aware objects unable to be compared here

* Address feedback

* Fix the newly added `modlog.create_case()` calls

Co-authored-by: jack1142 <6032823+jack1142@users.noreply.github.com>

redbot/core/bank.py

@@ -1,8 +1,8 @@
 from __future__ import annotations
 
 import asyncio
-import datetime
 import logging
+from datetime import datetime, timezone
 from typing import Union, List, Optional, TYPE_CHECKING, Literal
 from functools import wraps
 
@@ -109,7 +109,7 @@ class Account:
 
     This class should ONLY be instantiated by the bank itself."""
 
-    def __init__(self, name: str, balance: int, created_at: datetime.datetime):
+    def __init__(self, name: str, balance: int, created_at: datetime):
         self.name = name
         self.balance = balance
         self.created_at = created_at
@@ -117,25 +117,25 @@ class Account:
 
 def _encoded_current_time() -> int:
     """Get the current UTC time as a timestamp.
-    
+
     Returns
     -------
     int
         The current UTC timestamp.
 
     """
-    now = datetime.datetime.utcnow()
+    now = datetime.now(timezone.utc)
     return _encode_time(now)
 
 
-def _encode_time(time: datetime.datetime) -> int:
+def _encode_time(time: datetime) -> int:
     """Convert a datetime object to a serializable int.
-    
+
     Parameters
     ----------
     time : datetime.datetime
         The datetime to convert.
-        
+
     Returns
     -------
     int
@@ -146,21 +146,21 @@ def _encode_time(time: datetime.datetime) -> int:
     return ret
 
 
-def _decode_time(time: int) -> datetime.datetime:
+def _decode_time(time: int) -> datetime:
     """Convert a timestamp to a datetime object.
-    
+
     Parameters
     ----------
     time : int
         The timestamp to decode.
-        
+
     Returns
     -------
     datetime.datetime
         The datetime object from the timestamp.
 
     """
-    return datetime.datetime.utcfromtimestamp(time)
+    return datetime.utcfromtimestamp(time)
 
 
 async def get_balance(member: discord.Member) -> int: