Re-add the @pure annotations

These were removed in 691c2c816e but
should remain in the code base.

src/BinaryUtils.php

@@ -27,6 +27,8 @@ class BinaryUtils
      * @param int $clockSeq The 16-bit clock sequence value before the variant is applied
      *
      * @return int The 16-bit clock sequence multiplexed with the UUID variant
+     *
+     * @pure
      */
     public static function applyVariant(int $clockSeq): int
     {
@@ -42,6 +44,8 @@ class BinaryUtils
      * @param int $version The version to apply to the `time_hi` field
      *
      * @return int The 16-bit time_hi field of the timestamp multiplexed with the UUID version number
+     *
+     * @pure
      */
     public static function applyVersion(int $timeHi, int $version): int
     {