feat: add simplified Select extension methods to EntityIterator

Add overloads for Select that allow iterating over components without
manually building a QueryDescriptor, simplifying usage in systems.

examples/TicTacToe/Systems/RenderSystem.cs

@@ -18,8 +18,7 @@ public class RenderSystem : ISystem
                 grid[r, c] = '.';
 
         // Fill in placed marks using the iterator API.
-        var markQuery = world.Query().With<Cell>().With<Mark>().Build();
-        using var markIter = world.Select<Cell, Mark>(markQuery);
+        using var markIter = world.Select<Cell, Mark>();
         while (markIter.MoveNext())
         {
             grid[markIter.Current1.Row, markIter.Current1.Col] =

examples/TicTacToe/Systems/WinCheckSystem.cs

@@ -18,8 +18,7 @@ public class WinCheckSystem : ISystem
         // Build a 3×3 grid of marks using the iterator API.
         var grid = new Player[3, 3];
 
-        var query = world.Query().With<Cell>().With<Mark>().Build();
-        using var iter = world.Select<Cell, Mark>(query);
+        using var iter = world.Select<Cell, Mark>();
         while (iter.MoveNext())
         {
             grid[iter.Current1.Row, iter.Current1.Col] = iter.Current2.Player;