Refactor(Structure): Move ADTs into adt/ folder, rename spel.rkt to main.rkt

New structure groups all ADT modules under adt/ directory, removing
redundant adt- prefix from filenames. Library names now read as
(pacman-project adt position) etc. All imports updated accordingly.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

pacman-project/adt/position.rkt

@@ -0,0 +1,50 @@
+#lang r7rs
+
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+;;                              Position ADT                                 ;;
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+
+;; A position represents a location on the logical maze grid.
+;; Coordinates are in grid units (row, col), NOT pixels.
+
+(define-library (pacman-project adt position)
+  (import (scheme base))
+  (export make-position)
+
+  (begin
+
+    ;; make-position :: number, number -> position
+    ;; Creates a new position object with row and column on the grid.
+    (define (make-position row col)
+
+      ;; row! :: number -> /
+      (define (row! new-row)
+        (set! row new-row))
+
+      ;; col! :: number -> /
+      (define (col! new-col)
+        (set! col new-col))
+
+      ;; equal? :: position -> boolean
+      ;; Checks whether two positions have the same coordinates.
+      (define (equal? other)
+        (and (= row (other 'row))
+             (= col (other 'col))))
+
+      ;; move :: number, number -> position
+      ;; Returns a new position shifted by delta-row and delta-col.
+      (define (move delta-row delta-col)
+        (make-position (+ row delta-row)
+                       (+ col delta-col)))
+
+      ;; dispatch-position :: symbol -> any
+      (define (dispatch-position msg)
+        (cond ((eq? msg 'row) row)
+              ((eq? msg 'col) col)
+              ((eq? msg 'row!) row!)
+              ((eq? msg 'col!) col!)
+              ((eq? msg 'equal?) equal?)
+              ((eq? msg 'move) move)
+              (else (error "Position ADT -- Unknown message:" msg))))
+
+      dispatch-position)))