New sampler

[rtealwitter]

Motivation and Context

Simplify the sampling procedure using the approach described in "Provably Accurate Shapley Value Estimation via Leverage Score Sampling"

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Public API Changes

• [No] Public API changes

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How Has This Been Tested?

On the (very thorough) shapiq test suite, and on leverageshap

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Checklist

• [Yes] The changes have been tested locally.
• [N/A] Documentation has been updated (if the public API or usage changes).
• [?] An entry has been added to CHANGELOG.md (if relevant for users).
• [?] The code follows the project's style guidelines.
• [N/A] I have considered the impact of these changes on the public API.

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