Fix TEntity generic

[rincler]

Closes #520

[rincler]

@template TEntity of object

doesn't work for \Cycle\ORM\Iterator :(

Psalm emits the issues:

<file name="src/Iterator.php">
 <error line="123" column="16" severity="error" message="MixedReturnStatement: Could not infer a return type"/>
</file>
<file name="src/Relation/ManyToMany.php">
 <error line="148" column="24" severity="error" message="InvalidArgument: Argument 1 of SplObjectStorage::offsetSet expects never, but array-key|object provided"/>
</file>
<file name="src/Relation/ManyToMany.php">
 <error line="148" column="24" severity="error" message="InvalidArgument: Argument 1 of SplObjectStorage::offsetGet expects never, but array-key|object provided"/>
</file>
<file name="src/Relation/ManyToMany.php">
 <error line="[31](https://github.com/rincler/orm/actions/runs/15075752236/job/42382664586#step:11:32)9" column="24" severity="error" message="InvalidArgument: Argument 1 of SplObjectStorage::offsetSet expects never, but array-key|object provided"/>
</file>
<file name="src/Relation/ManyToMany.php">
 <error line="319" column="24" severity="error" message="InvalidArgument: Argument 1 of SplObjectStorage::offsetGet expects never, but array-key|object provided"/>
</file>
<file name="src/Select.php">
 <error line="395" column="16" severity="error" message="InvalidReturnType: The declared return type &apos;Cycle\ORM\Iterator&lt;TEntity:Cycle\ORM\Select as object&gt;&apos; for Cycle\ORM\Select::getIterator is incorrect, got &apos;Cycle\ORM\Iterator&apos;"/>
</file>
<file name="src/Select.php">
 <error line="[40](https://github.com/rincler/orm/actions/runs/15075752236/job/42382664586#step:11:41)2" column="16" severity="error" message="InvalidReturnStatement: The inferred type &apos;Cycle\ORM\Iterator&apos; does not match the declared return type &apos;Cycle\ORM\Iterator&lt;TEntity:Cycle\ORM\Select as object&gt;&apos; for Cycle\ORM\Select::getIterator"/>
</file>