TUniqueValues: fix methods signatures

src/Collections/TUniqueValues.php

@@ -12,7 +12,7 @@ trait TUniqueValues {
     /**
      * @inheritDoc
      */
-    protected function _set (int|string $key, mixed $value): self {
+    protected function _set ($key, $value): static {
         if ($this->contains($value)) {
             return $this;
         }
@@ -23,7 +23,7 @@ trait TUniqueValues {
     /**
      * @inheritDoc
      */
-    protected function _add (mixed ...$values): self {
+    protected function _add (...$values): static {
         foreach ($values as $value) {
             if ($this->contains($value)) {
                 continue;