feat(core): add board geometry and piece encoding

Types.scala

@@ -0,0 +1,65 @@
+package gambit
+
+object Color:
+  val White = 0
+  val Black = 1
+  inline def opposite(c: Int): Int = c ^ 1
+
+object Piece:
+  val Empty = 0
+  val Pawn = 1
+  val Knight = 2
+  val Bishop = 3
+  val Rook = 4
+  val Queen = 5
+  val King = 6
+
+  inline def make(color: Int, pieceType: Int): Int = (color << 3) | pieceType
+  inline def typeOf(piece: Int): Int = piece & 7
+  inline def colorOf(piece: Int): Int = piece >> 3
+
+  val WhitePawn = make(Color.White, Pawn)
+  val WhiteKnight = make(Color.White, Knight)
+  val WhiteBishop = make(Color.White, Bishop)
+  val WhiteRook = make(Color.White, Rook)
+  val WhiteQueen = make(Color.White, Queen)
+  val WhiteKing = make(Color.White, King)
+  val BlackPawn = make(Color.Black, Pawn)
+  val BlackKnight = make(Color.Black, Knight)
+  val BlackBishop = make(Color.Black, Bishop)
+  val BlackRook = make(Color.Black, Rook)
+  val BlackQueen = make(Color.Black, Queen)
+  val BlackKing = make(Color.Black, King)
+
+object Square:
+  inline def make(file: Int, rank: Int): Int = rank * 16 + file
+  inline def fileOf(sq: Int): Int = sq & 7
+  inline def rankOf(sq: Int): Int = sq >> 4
+  inline def onBoard(sq: Int): Boolean = (sq & 0x88) == 0
+
+  def name(sq: Int): String =
+    val file = ('a' + fileOf(sq)).toChar
+    val rank = ('1' + rankOf(sq)).toChar
+    s"$file$rank"
+
+  def fromName(s: String): Int = make(s(0) - 'a', s(1) - '1')
+
+object Castling:
+  val WhiteKing = 1
+  val WhiteQueen = 2
+  val BlackKing = 4
+  val BlackQueen = 8
+
+  val mask: Array[Int] = Array.fill(128)(15)
+  mask(Square.make(4, 0)) = 15 & ~(WhiteKing | WhiteQueen)
+  mask(Square.make(7, 0)) = 15 & ~WhiteKing
+  mask(Square.make(0, 0)) = 15 & ~WhiteQueen
+  mask(Square.make(4, 7)) = 15 & ~(BlackKing | BlackQueen)
+  mask(Square.make(7, 7)) = 15 & ~BlackKing
+  mask(Square.make(0, 7)) = 15 & ~BlackQueen
+
+object Directions:
+  val knight: Array[Int] = Array(33, 31, 18, 14, -14, -18, -31, -33)
+  val bishop: Array[Int] = Array(17, 15, -15, -17)
+  val rook: Array[Int] = Array(16, 1, -1, -16)
+  val king: Array[Int] = Array(17, 16, 15, 1, -1, -15, -16, -17)