implement image_uris.retrieve() for eusc-de-east-1 region

**Describe the feature you'd like**
use pytorch uri from sagemaker within the ESC region (european sovereign cloud)

Start by locating image_uris.retrieve() and the existing PyTorch URI handling, then inspect how regions are represented. Check the SageMaker documentation or current tests for image URI retrieval and determine the expected behavior for eusc-de-east-1. Done means PyTorch image URIs can be retrieved for that region and the relevant tests pass.

Written by the indexing model from the issue text.