[TASK] Improve comments and phpdoc blocks in PageRepository

* fix comment line lengths to improve readability and meet the CGL
* add some additional line breaks in comments to improve readability
* add missing @throws annotations in phpdoc blocks
* add missing @var annotations in phpdoc blocks

Resolves: #57859
Releases: 6.2
Change-Id: I311c6c858c8810b4a8906918378629aef5e1ebc8
Reviewed-on: https://review.typo3.org/29425
Reviewed-by: Oliver Klee
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn