`RotationWrapper` unnecessarily calculates core of block instead of using `DataSetBlock.data_unpadded`

As the title says, the following logic is unnecessary and likely can be made tidier by using `block.data_unpadded`: https://github.com/DiamondLightSource/httomo/blob/5c5c57b4290ed3bc3fee806d1c78419a4a8cb7a5/httomo/method_wrappers/rotation.py#L154-L161

Plus, the logic to extract the core out of a padded block is already tested for `DataSetBlock.data_unpadded`: https://github.com/DiamondLightSource/httomo/blob/5c5c57b4290ed3bc3fee806d1c78419a4a8cb7a5/tests/runner/test_dataset_block.py#L532-L552

whereas the code extracting the block's core in the rotation wrapper isn't.