Random spontaneous cleanup PR (#25131)

* Use new Subs.CVar helper

Removes manual config OnValueChanged calls, removes need to remember to manually unsubscribe.

This both reduces boilerplate and fixes many issues where subscriptions weren't removed on entity system shutdown.

* Fix a bunch of warnings

* More warning fixes

* Use new DateTime serializer to get rid of ISerializationHooks in changelog code.

* Get rid of some more ISerializationHooks for enums

* And a little more

* Apply suggestions from code review

Co-authored-by: 0x6273 <0x40@keemail.me>

---------

Co-authored-by: 0x6273 <0x40@keemail.me>

Content.Server/Administration/Commands/BanCommand.cs

@@ -18,6 +18,7 @@ public sealed class BanCommand : LocalizedCommands
     [Dependency] private readonly IBanManager _bans = default!;
     [Dependency] private readonly IConfigurationManager _cfg = default!;
     [Dependency] private readonly IPlayerManager _playerManager = default!;
+    [Dependency] private readonly ILogManager _logManager = default!;
 
     public override string Command => "ban";
 
@@ -28,7 +29,8 @@ public sealed class BanCommand : LocalizedCommands
         uint minutes;
         if (!Enum.TryParse(_cfg.GetCVar(CCVars.ServerBanDefaultSeverity), out NoteSeverity severity))
         {
-            Logger.WarningS("admin.server_ban", "Server ban severity could not be parsed from config! Defaulting to high.");
+            _logManager.GetSawmill("admin.server_ban")
+                .Warning("Server ban severity could not be parsed from config! Defaulting to high.");
             severity = NoteSeverity.High;
         }