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.Shared/Clothing/EntitySystems/StealthClothingSystem.cs

@@ -114,7 +114,7 @@ public sealed class StealthClothingSystem : EntitySystem
 /// <summary>
 /// Raised on the stealth clothing when attempting to add an action.
 /// </summary>
-public class AddStealthActionEvent : CancellableEntityEventArgs
+public sealed class AddStealthActionEvent : CancellableEntityEventArgs
 {
     /// <summary>
     /// User that equipped the stealth clothing.
@@ -130,7 +130,7 @@ public class AddStealthActionEvent : CancellableEntityEventArgs
 /// <summary>
 /// Raised on the stealth clothing when the user is attemping to enable it.
 /// </summary>
-public class AttemptStealthEvent : CancellableEntityEventArgs
+public sealed class AttemptStealthEvent : CancellableEntityEventArgs
 {
     /// <summary>
     /// User that is attempting to enable the stealth clothing.