feat(model): create concept of graph for map

src/main/scala/scatan/model/map/UndirectedGraph.scala

@@ -0,0 +1,28 @@
+package scatan.model.map
+
+/** A graph is a set of nodes and edges.
+  */
+trait UndirectedGraph[Node, Edge <: UnorderedPair[Node, Node]]:
+
+  /** @return
+    *   the set of nodes
+    */
+  def nodes: Set[Node]
+
+  /** @return
+    *   the set of edges
+    */
+  def edges: Set[Edge]
+
+/** An unordered pair of elements.
+  * @param a
+  *   an element
+  * @param b
+  *   another element
+  */
+case class UnorderedPair[A, B](a: A, b: B):
+  override def equals(that: Any): Boolean = that match
+    case UnorderedPair(a1, b1) => (a == a1 && b == b1) || (a == b1 && b == a1)
+    case _                     => false
+
+  override def hashCode: Int = a.hashCode + b.hashCode

src/test/scala/scatan/model/map/UnorderedPairTest.scala

@@ -0,0 +1,41 @@
+package scatan.model.map
+
+import cats.kernel.Monoid
+import cats.syntax.semigroup.*
+import org.scalatestplus.scalacheck.ScalaCheckPropertyChecks
+import scatan.BaseTest
+import scatan.model.map.Hexagon.given
+import scatan.model.map.HexTiledMap.*
+
+class UnorderedPairTest extends BaseTest with ScalaCheckPropertyChecks:
+
+  "A UnorderedPair" should "have 2 elements" in {
+    assertCompiles("UnorderedPair(0, 0)")
+    assertDoesNotCompile("UnorderedPair()")
+  }
+
+  it should "be equals based on its elements" in {
+    forAll { (a: Int, b: Int) =>
+      val pair1 = UnorderedPair(a, b)
+      val pair2 = UnorderedPair(a, b)
+      pair1 shouldBe pair2
+    }
+  }
+
+  it should "be equals also in reverse order of its elements" in {
+    forAll { (a: Int, b: Int) =>
+      val pair1 = UnorderedPair(a, b)
+      val pair2 = UnorderedPair(b, a)
+      pair1 shouldBe pair2
+    }
+  }
+
+  it should "be not equals if its elements are different" in {
+    forAll { (a1: Int, b1: Int, a2: Int, b2: Int) =>
+      whenever(a1 != a2 || b1 != b2) {
+        val pair1 = UnorderedPair(a1, b1)
+        val pair2 = UnorderedPair(a2, b2)
+        pair1 should not be pair2
+      }
+    }
+  }