Add device-agnostic process group wrappers for distributed setup initialization

[AnantGulati]

As an extension of RFC #257

The goal of this PR is to enable device-agnostic distributed setup initialization.

I've created two new classes:

1. ProcessGroupAccelerator
2. ProcessGroupBabyAccelerator

These classes automatically route to the appropriate device-specific implementation using torch.accelerator:

• CUDA → ProcessGroupNCCL / ProcessGroupBabyNCCL
• XPU → ProcessGroupXCCL / ProcessGroupBabyXCCL

I've added test cases to demonstrate and validate this functionality.

Future PRs will convert more test cases and code files to use this device-agnostic approach, reducing manual overhead and enabling greater flexibility and code reuse.

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[AnantGulati]

@d4l3k @H-Huang @tushar00jain Could you please review or allocate the appropriate reviewer for this PR

Thanks