Add PyTorch MPS device support

[Malek-AlAbed]

Description

Closes #

Type of Change

• Bug fix
• Hotfix for a breaking change on main
• New feature
• Refactor
• Interface to external software
• DevOps / CI
• Documentation
• Other — please describe:

Checklist

• This PR targets the develop branch (or main for hotfixes and documentation only).
• The pre-commit hook has been run and all files are formatted (ruff).
• Unit tests pass locally (pytest test).
• New or changed code is covered by tests; coverage has not dropped significantly.
• CHANGELOG.md has been updated in the [UNRELEASED] section following Keep a Changelog conventions.

Testing

Added a unit test function covering the MPS device selection logic to the script test/core/xp_utils/test_initialization.py

pytest test/core/xp_utils/test_initialization.py

Additional Notes

This PR adds support for Apple Metal Performance Shaders (MPS) devices when using the PyTorch backend.

Changes:

• Detect PyTorch MPS availability in choose_device()
• Return "mps" when MPS is available

[Malek-AlAbed]

There is more to be done regarding the variables dtype before implementing it
MPS does not support double, and having the CT in float32 is not enough , it should go within calculating the dose matrix