Revert "PC^2 does not send timelimits for problems, so make them optional."

We want to follow the spec and not be lenient for this import error. We
have a separate branch for the customizations for PC2 so when we shadow
them we can easily cherry-pick those.

This reverts commit a25d24b.

Author: vmcj

webapp/src/DataTransferObject/Shadowing/ProblemEvent.php

@@ -7,7 +7,7 @@ class ProblemEvent implements EventData
     public function __construct(
         public readonly string $id,
         public readonly string $name,
-        public readonly ?int $timeLimit,
+        public readonly int $timeLimit,
         public readonly ?string $label,
         public readonly ?string $rgb,
     ) {}

webapp/src/Service/ExternalContestSourceService.php

@@ -1024,13 +1024,10 @@ protected function validateAndUpdateProblem(Event $event, EventData $data): void
         $this->removeWarning($event->type, $data->id, ExternalSourceWarning::TYPE_ENTITY_NOT_FOUND);
 
         $toCheckProblem = [
-            'name' => $data->name,
+            'name'      => $data->name,
+            'timelimit' => $data->timeLimit,
         ];
 
-        if ($data->timeLimit !== null) {
-            $toCheckProblem['timelimit'] = $data->timeLimit;
-        }
-
         if ($contestProblem->getShortname() !== $data->label) {
             $this->logger->warning(
                 'Contest problem short name does not match between feed (%s) and local (%s), updating',