Increase PHPStan levels and update code to resolve issues found

src/Generator/DefaultTimeGenerator.php

@@ -92,7 +92,7 @@ class DefaultTimeGenerator implements TimeGeneratorInterface
         // Create a 60-bit time value as a count of 100-nanosecond intervals
         // since 00:00:00.00, 15 October 1582
         $timeOfDay = $this->timeProvider->currentTime();
-        $uuidTime = $this->timeConverter->calculateTime($timeOfDay['sec'], $timeOfDay['usec']);
+        $uuidTime = $this->timeConverter->calculateTime((string) $timeOfDay['sec'], (string) $timeOfDay['usec']);
 
         $timeHi = BinaryUtils::applyVersion($uuidTime['hi'], 1);
         $clockSeqHi = BinaryUtils::applyVariant($clockSeq >> 8);
@@ -109,14 +109,14 @@ class DefaultTimeGenerator implements TimeGeneratorInterface
             ]
         );
 
-        return hex2bin($hex);
+        return (string) hex2bin($hex);
     }
 
     /**
      * Uses the node provider given when constructing this instance to get
      * the node ID (usually a MAC address)
      *
-     * @param string|int $node A node value that may be used to override the node provider
+     * @param string|int|null $node A node value that may be used to override the node provider
      * @return string Hexadecimal representation of the node ID
      * @throws InvalidArgumentException
      * @throws Exception