Update coding style to include PSR-12, among other options

This also includes heavy use of slevomat/coding-standard to apply
various checks to the code, based on maintainer (me) preference.

src/Uuid.php

@@ -569,9 +569,6 @@ class Uuid implements UuidInterface
         return (int) hexdec($this->getTimestampHex());
     }
 
-    /**
-     * @inheritdoc
-     */
     public function getTimestampHex(): string
     {
         if ($this->getVersion() !== 1) {