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 87%. Comparing base (37f559e) to head (e013cb2).

Additional details and impacted files

@@           Coverage Diff           @@
##           master   #20872   +/-   ##
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  Coverage      87%      87%           
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  Files         268      268           
  Lines       23460    23469    +9     
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+ Hits        20399    20413   +14     
+ Misses       3061     3056    -5     

[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

[stale]

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[AlexandrByzov]

Is there anything else that can be done for this MR @Borda ? I will be glad to work on it further