[board] Directly use PlacedPiece in the position! macro

Avoids having to also import the piece! macro to use position!.

board/src/macros.rs

@@ -4,7 +4,14 @@
 macro_rules! position {
     [$($color:ident $shape:ident on $square:ident),* $(,)?] => {
         $crate::PositionBuilder::new()
-            $(.place_piece(piece!($color $shape on $square)))*
+            $(.place_piece(
+                chessfriend_core::PlacedPiece::new(
+                    chessfriend_core::Piece::new(
+                        chessfriend_core::Color::$color,
+                        chessfriend_core::Shape::$shape),
+                    chessfriend_core::Square::$square
+                )
+            ))*
             .build()
     };
 }