Forced load imbalance

[nanz-nv]

What does this PR do ?

This PR tries to add a utility to force load imbalance among experts. dev PR #2917

⚠️ 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

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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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(Step 2): Collect the expert reviewers reviews

1. Attach the Expert Review label when your PR is ready for review.
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⚠️ Only proceed to the next step once all reviewers have approved, merge-conflict are resolved and the CI is passing.
Final Review might get declined if these requirements are not fulfilled.

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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.

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[Phlip79]

/ok to test c96049d

[Phlip79]

@nanz-nv please fix test error

[yashaswikarnati]

some nits;

1. could we make this more explicit in the naming - moe_router_expert_bias_force_random
2. curious why this is experimental

[Victarry]

/ok to test 9ff4db8