common strategy simplification

[dimapihtar]

What does this PR do ?

Simplifies common.py strategy as a part of checkpointing simplification by droping LoadCommonStrategy, SaveCommonStrategy, TorchCommonSaveStrategy, TorchCommonLoadStrategy and their substituion with a simplier functions.

⚠️ For major changes (either in lines of code or in its impact), please make sure to first share a design doc with the team. If you're unsure what's the best way to do so, contact the @mcore-oncall.

Contribution process

flowchart LR
    A[Pre-checks] --> B[PR Tests]
    subgraph Code Review/Approval
        C1[Expert Review] --> C2[Final Review]
    end
    B --> C1
    C2 --> D[Merge]

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Pre-checks

• I want this PR in a versioned release and have added the appropriate Milestone (e.g., Core 0.8)
• I have added relevant unit tests
• I have added relevant functional tests
• I have added proper typing to my code Typing guidelines
• I have added relevant documentation
• I have run the autoformatter.sh on my PR

Code review

The following process is enforced via the CODEOWNERS file for changes into megatron/core. For changes outside of megatron/core, it is up to the PR author whether or not to tag the Final Reviewer team.

For MRs into `main` branch

Feel free to message or comment the @mcore-oncall to help accelerate your merge into main. The less complex your PR is, the faster it will be approved and merged!

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1. Attach the Expert Review label when your PR is ready for review.
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Final Review might get declined if these requirements are not fulfilled.

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If this PR also needs to be merged into core_r* release branches, after this PR has been merged, select Cherry-pick to open a new PR into the release branch.

For MRs into `dev` branch

The proposed review process for `dev` branch is under active discussion.

MRs are mergable after one approval by either eharper@nvidia.com or zijiey@nvidia.com.

Merging your PR

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[copy-pr-bot]

This pull request requires additional validation before any workflows can run on NVIDIA's runners.

Pull request vetters can view their responsibilities here.

Contributors can view more details about this message here.

[dimapihtar]

/ok to test dde7dcc

[dimapihtar]

/ok to test f0a3803

[dimapihtar]

/ok to test 6f3f7d1

[dimapihtar]

/ok to test 7813b47

[dimapihtar]

/ok to test da4008e

[dimapihtar]

/ok to test c7c8477

[dimapihtar]

/ok to test f7d7f55

[svcnvidia-nemo-ci]

🔄 Merge queue validation started!

You can track the progress here: https://github.com/NVIDIA/Megatron-LM/actions/runs/23361119806