[BUGFIX] Fix and improve type annotations of the Repository base class

This helps reduce warnings when extensions are type-checked with PHPStan.

Resolves: #97820
Releases: main, 11.5

Change-Id: Iee5cd28402d9e33af0bfaa34815552ba331718ee
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/74991


Tested-by: core-ci <typo3@b13.com>
Tested-by: Benni Mack <benni@typo3.org>
Tested-by: Nikita Hovratov <nikita.h@live.de>
Reviewed-by: Benni Mack <benni@typo3.org>
Reviewed-by: Nikita Hovratov <nikita.h@live.de>