Allow unstricted model loading

[antoine-tran]

We want to extend the ModelLoader API by allowing load checkpoints with incomplete parameters to a registered model. This is useful where different model blocks are delivered in different checkpoints (for example, to save spaces), as in the cases with the V-JEPA checkpoints (https://github.com/facebookresearch/jepa)

Fixes #{issue number}

Does your PR introduce any breaking changes? If yes, please list them:
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• Was the content of this PR discussed and approved via a GitHub issue? (no need for typos or documentation improvements)
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[cbalioglu]

LGTM!