Refactor model_provider to model_builder format for ModelOpt examples

[AAnoosheh]

What does this PR do ?

ModelOpt path still used model_provider without a builder function, so it's been updated to be synced with the standard code path.

⚠️ For major changes (either in lines of code or in its impact), please make sure to first share discuss a design-doc with the team.

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 `dev` branch

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[AAnoosheh]

/ok to test a1ad1f9