Complete return types for Tasks and Batches endpoints

[Strift]

The Tasks and Batches endpoints have missing return types or unresolved TODOs regarding return values.

Files & Actions:

1. src/Endpoints/Tasks.php

   • all(array $query = []): Resolve the existing TODO (// @todo: must return array<Task>). Ensure it returns TasksResults or a strongly typed array.

2. src/Endpoints/Batches.php

   • get(int $batchUid): Add PHPDoc return type or return a Batch DTO.
   • all(array $query = []): Update to return BatchesResults or add explicit PHPDoc.