Add map function implementation for Set

Author: jules-iti

src/Set.php

@@ -258,6 +258,22 @@ public function last()
         return $this->table->last()->key;
     }
 
+    /**
+     * Returns a new set using the results of applying a callback to each
+     * value.
+     *
+     * @param callable $callback
+     *
+     * @return Set
+     *
+     * @template TNewValue
+     * @psalm-param callable(TValue): TNewValue $callback
+     * @psalm-return Set<TNewValue>
+     */
+    public function map(callable $callback) {
+        return new self(array_map($callback, $this->toArray()));
+    }
+
     /**
      * Iteratively reduces the set to a single value using a callback.
      *