refactor: NCS-19 Currying (#18)

Summary

  - Curried candidateMoves, legalMoves, and applyMove in the RuleSet trait to separate (context) as the world being
  operated on from the computation parameter
  - Updated DefaultRules overrides and all internal call sites
  - Updated all external call sites: GameEngine, PgnParser, PgnExporter, ChessBoardView, and all affected tests

  Test plan

  - All existing tests pass (./gradlew build)
  - No behaviour changes — pure style refactoring, existing test suite is the regression guard

Co-authored-by: LQ63 <lkhermann@web.de>
Reviewed-on: #18
Reviewed-by: Janis <janis-e@gmx.de>
Co-authored-by: Leon Hermann <lq@blackhole.local>
Co-committed-by: Leon Hermann <lq@blackhole.local>

modules/rule/src/main/scala/de/nowchess/rules/RuleSet.scala

@@ -9,10 +9,10 @@ import de.nowchess.api.move.Move
  */
 trait RuleSet:
   /** All pseudo-legal moves for the piece on `square` (ignores check). */
-  def candidateMoves(context: GameContext, square: Square): List[Move]
+  def candidateMoves(context: GameContext)(square: Square): List[Move]
 
   /** Legal moves for `square`: candidates that don't leave own king in check. */
-  def legalMoves(context: GameContext, square: Square): List[Move]
+  def legalMoves(context: GameContext)(square: Square): List[Move]
 
   /** All legal moves for the side to move. */
   def allLegalMoves(context: GameContext): List[Move]
@@ -36,4 +36,4 @@ trait RuleSet:
    *  Handles all special move types: castling, en passant, promotion.
    *  Updates castling rights, en passant square, half-move clock, turn, and move history.
    */
-  def applyMove(context: GameContext, move: Move): GameContext
+  def applyMove(context: GameContext)(move: Move): GameContext

modules/rule/src/main/scala/de/nowchess/rules/sets/DefaultRules.scala

@@ -26,7 +26,7 @@ object DefaultRules extends RuleSet:
 
   // ── Public API ─────────────────────────────────────────────────────
 
-  override def candidateMoves(context: GameContext, square: Square): List[Move] =
+  override def candidateMoves(context: GameContext)(square: Square): List[Move] =
     context.board.pieceAt(square).fold(List.empty[Move]) { piece =>
       if piece.color != context.turn then List.empty[Move]
       else piece.pieceType match
@@ -38,13 +38,13 @@ object DefaultRules extends RuleSet:
         case PieceType.King => kingCandidates(context, square, piece.color)
     }
 
-  override def legalMoves(context: GameContext, square: Square): List[Move] =
-    candidateMoves(context, square).filter { move =>
+  override def legalMoves(context: GameContext)(square: Square): List[Move] =
+    candidateMoves(context)(square).filter { move =>
       !leavesKingInCheck(context, move)
     }
 
   override def allLegalMoves(context: GameContext): List[Move] =
-    Square.all.flatMap(sq => legalMoves(context, sq)).toList
+    Square.all.flatMap(sq => legalMoves(context)(sq)).toList
 
   override def isCheck(context: GameContext): Boolean =
     kingSquare(context.board, context.turn)
@@ -284,7 +284,7 @@ object DefaultRules extends RuleSet:
 
   // ── Move application ───────────────────────────────────────────────
 
-  override def applyMove(context: GameContext, move: Move): GameContext =
+  override def applyMove(context: GameContext)(move: Move): GameContext =
     val color = context.turn
     val board  = context.board