feat(core): add zobrist hashing keys

Zobrist.scala

@@ -0,0 +1,9 @@
+package gambit
+
+object Zobrist:
+  private val rng = new scala.util.Random(0x9E3779B97F4A7C15L)
+
+  val pieceKeys: Array[Array[Long]] = Array.fill(15, 128)(rng.nextLong())
+  val sideKey: Long = rng.nextLong()
+  val castleKeys: Array[Long] = Array.fill(16)(rng.nextLong())
+  val epFileKeys: Array[Long] = Array.fill(8)(rng.nextLong())