add Interface Set. (#13)

* Add Deque Interface and Corresponding Tests

- Created Deque interface extending Queue interface to define additional methods for double-ended queues.
- Added methods: addFirst, removeLast, and peekLast to the Deque interface.
- Implemented unit tests for Deque interface to ensure proper contract implementation.

Interface:
- KaririCode\Contract\DataStructure\Deque

Tests:
- KaririCode\Contract\Tests\DataStructure\DequeTest

* add Interface Set

* nomalize to PSR

* adjust comments

Author: walmir-silva

src/DataStructure/Behavioral/IterableCollection.php

@@ -4,8 +4,6 @@
 
 namespace KaririCode\Contract\DataStructure\Behavioral;
 
-use KaririCode\Contract\DataStructure\Behavioral\Iterator;
-
 /**
  * Interface IterableCollection.
  *

src/DataStructure/DequeTest.php

@@ -59,7 +59,6 @@ public function testPeekLast(): void
 
     public function testIsEmpty(): void
     {
-
         $mock = $this->createMock(Deque::class);
         $mock->method('isEmpty')->willReturn(true);
 

src/DataStructure/Set.php

@@ -0,0 +1,66 @@
+<?php
+
+declare(strict_types=1);
+
+namespace KaririCode\Contract\DataStructure;
+
+/**
+ * Interface Set.
+ *
+ * Defines the contract for set data structures, which do not allow duplicate elements.
+ *
+ * @category  Interfaces
+ *
+ * @author    Walmir Silva <walmir.silva@kariricode.org>
+ * @license   MIT
+ *
+ * @see       https://kariricode.org/
+ */
+interface Set
+{
+    /**
+     * Adds an element to the set.
+     *
+     * @param mixed $element The element to add
+     *
+     * @return bool True if the element was added, false if it was already present
+     */
+    public function add(mixed $element): bool;
+
+    /**
+     * Removes an element from the set.
+     *
+     * @param mixed $element The element to remove
+     *
+     * @return bool True if the element was removed, false if it was not present
+     */
+    public function remove(mixed $element): bool;
+
+    /**
+     * Checks if the set contains a specific element.
+     *
+     * @param mixed $element The element to check for
+     *
+     * @return bool True if the element is present, false otherwise
+     */
+    public function contains(mixed $element): bool;
+
+    /**
+     * Removes all elements from the set.
+     */
+    public function clear(): void;
+
+    /**
+     * Returns the number of elements in the set.
+     *
+     * @return int The number of elements in the set
+     */
+    public function size(): int;
+
+    /**
+     * Checks if the set is empty.
+     *
+     * @return bool True if the set is empty, false otherwise
+     */
+    public function isEmpty(): bool;
+}