Seal/abstract/virtual everything (#6739)

Content.Server/Atmos/TileAtmosphere.cs

@@ -11,7 +11,7 @@ namespace Content.Server.Atmos
     ///     Internal Atmos class that stores data about the atmosphere in a grid.
     ///     You shouldn't use this directly, use <see cref="AtmosphereSystem"/> instead.
     /// </summary>
-    public class TileAtmosphere : IGasMixtureHolder
+    public sealed class TileAtmosphere : IGasMixtureHolder
     {
         [ViewVariables]
         public int ArchivedCycle;