Fix Hang in tests

[wdykas]

What does this PR do ?

destroy_model_parallel now destroys each NCCL subgroup tracked in _global_process_group_list (skipping the default at index 0) before nulling the python references. Without this, ProcessGroupNCCL objects and their NVLS multicast memory bindings accumulated across re-init cycles, eventually exhausting the NVLS pool and surfacing as a misleading transport/nvls.cc out of memory error.

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[wdykas]

/ok to test 153003a

[ericharper]

@wdykas , is the PR ready? Still marked as draft.

[wdykas]

@wdykas , is the PR ready? Still marked as draft.

I will take it out of draft when I have merged in main which I am trying now

[wdykas]

/ok to test 6b6510f

[wdykas]

@wdykas , is the PR ready? Still marked as draft.

just marked it as not draft

[ericharper]

/ok to test 6b6510f

[wdykas]

/ok to test e2fc2f0

[wdykas]

/ok to test 1170273

[wdykas]

/ok to test 9e4a1f3

[wdykas]

/ok to test 60f1997

[wdykas]

/ok to test 60f1997

[svcnvidia-nemo-ci]

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