Move EntityNotFoundException out of World class

src/gaemstone.ECS/EntityPath.cs

@@ -149,7 +149,7 @@ public class EntityPath
 				if (!throwOnNotFound) return Entity.None;
 
 				var startStr = EntityRef.CreateOrNull(world, start)?.GetFullPath().ToString() ?? start.ToString();
-				throw new World.EntityNotFoundException(
+				throw new EntityNotFoundException(
 					   start.IsNone     ? $"Entity at '{path}' not found"
 					: (start == parent) ? $"Child entity of '{startStr}' at '{path}' not found"
 					                    : $"Entity at scope '{startStr}' at '{path}' not found");

src/gaemstone.ECS/World+Lookup.cs

@@ -32,8 +32,7 @@ public unsafe partial class World
 	public EntityRef LookupBySymbolOrThrow(string symbol)
 		=> LookupBySymbol(symbol) ?? throw new EntityNotFoundException(
 			$"Entity with symbol '{symbol}' not found");
+}
 
-
+public class EntityNotFoundException : Exception
-	public class EntityNotFoundException : Exception
 	{ public EntityNotFoundException(string message) : base(message) {  } }
-}