Add unit tests for areas plugin

game/plugin/areas/src/Area.kt

@@ -0,0 +1,27 @@
+package org.apollo.game.plugins.area
+
+import org.apollo.game.model.Position
+import org.apollo.game.plugins.api.Position.component1
+import org.apollo.game.plugins.api.Position.component2
+import org.apollo.game.plugins.api.Position.component3
+
+/**
+ * An area in the game world.
+ */
+interface Area {
+
+    /**
+     * Returns whether or not the specified [Position] is inside this [Area].
+     */
+    operator fun contains(position: Position): Boolean
+
+}
+
+internal class RectangularArea(private val x: IntRange, private val y: IntRange, private val height: Int) : Area {
+
+    override operator fun contains(position: Position): Boolean {
+        val (x, y, z) = position
+        return x in this.x && y in this.y && z == height
+    }
+
+}