Adds bufferSize API to be able to derive memory occupied by a single model

[aleroot]

Proposed changes

This is the basic memory for model API based on ml-explore/mlx-c#131 --> ml-explore/mlx#4436

This pull request needs to wait a new version of mlx-c being released and pinned in mlx-c see this PR.

@davidkoski when this will be merged, I have a new memory footprint API ready for mlx-swift-lm, let me know if you think it is useful I can post it now and you can have a look already, otherwise I will wait for the new release.

Checklist

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• I have added tests that prove my fix is effective or that my feature works
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