[board] Move position builders into a builders module

Move PositionBuilder to position_builder.rs and export it from the builders module.

board/src/position/builders/mod.rs

@@ -0,0 +1,5 @@
+// Eryn Wells <eryn@erynwells.me>
+
+mod position_builder;
+
+pub use position_builder::Builder as PositionBuilder;

board/src/position/builders/position_builder.rs

@@ -1,9 +1,11 @@
 // Eryn Wells <eryn@erynwells.me>
 
-use super::{flags::Flags, piece_sets::PieceBitBoards};
 use crate::{
+    bitboard::BitBoardBuilder,
     piece::{PlacedPiece, Shape},
-    square::Rank,
+    position::{flags::Flags, piece_sets::PieceBitBoards, BoardSide},
+    r#move::Castle,
+    square::{Direction, Rank},
     BitBoard, Color, MakeMoveError, Move, Piece, Position, Square,
 };
 use std::collections::BTreeMap;
@@ -30,7 +32,7 @@ impl Builder {
             self.kings[color_index] = square;
         }
 
-        self.pieces.insert(square, piece.piece());
+        self.pieces.insert(square, *piece.piece());
 
         self
     }
@@ -81,3 +83,15 @@ impl Default for Builder {
         }
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use crate::PositionBuilder;
+
+    #[test]
+    fn place_piece() {
+        let piece = piece!(White Queen on E4);
+        let builder = PositionBuilder::new().place_piece(piece).build();
+        assert_eq!(builder.piece_on_square(piece.square()), Some(piece));
+    }
+}