bugfix: add support for global_ordinal, local_ordinal, world_size in xla

[AlexandrByzov]

What does this PR do?

PyTorch XLA has deprecated several methods in PyTorch 2.7:

• Remove torch_xla.core.xla_model.xrt_world_size, replace with torch_xla.runtime.world_size
• Remove torch_xla.core.xla_model.get_ordinal, replace with torch_xla.runtime.global_ordinal

See here

Fixes #20852

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📚 Documentation preview 📚: https://pytorch-lightning--20872.org.readthedocs.build/en/20872/

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 86%. Comparing base (6675932) to head (140ac0b).
Report is 29 commits behind head on master.

Additional details and impacted files

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- Coverage      87%      86%    -0%     
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  Files         268      268            
  Lines       23411    23451    +40     
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- Hits        20360    20278    -82     
- Misses       3051     3173   +122     

[Borda]

thank you for this finding!
could you pls add test to cover this new behaviour?
can this XLA be also run without TPU?

[AlexandrByzov]

thank you for this finding! could you pls add test to cover this new behaviour? can this XLA be also run without TPU?

Thank you for taking the time to review. I implemented a test with mocks, because as far as I understand torch_xla is not used in tests without TPU. Generally, it is very much possible to use XLA with CPU or even GPU, but this will require a large change in tests and probably a separate issue/s