Improved parallel logging of learning rate

[jstjohn]

What does this PR do ?

Rewrite of how we handle parallel logging of the learning rate. Taking advantage of some megatron functionality including making use of the learning rate stored in empty param groups (eg those that have weights on other ranks). This PR replaces #3258

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flowchart LR
    A[Pre-checks] --> B[PR Tests]
    subgraph Code Review/Approval
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    end
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[jstjohn]

/ok to test fae5e57

[BoxiangW]

LGTM, thx

[jstjohn]

/ok to test cd66f91

[ko3n1g]

validated on the gpt release run

[ko3n1g]

🔄 Merge queue validation started!

You can track the progress here: https://github.com/NVIDIA/Megatron-LM/actions/runs/21927774607

[ko3n1g]

🔄 Merge queue validation started!

You can track the progress here: https://github.com/NVIDIA/Megatron-LM/actions/runs/21928298859

[ko3n1g]

🔄 Merge queue validation started!

You can track the progress here: https://github.com/NVIDIA/Megatron-LM/actions/runs/21945988636