Add size 256 checkpoint

[arr00]

Fixes #????

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• [ ] Tests
• [ ] Documentation
• [ ] Changeset entry (run npx changeset add)

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Latest commit: df4985a9d008687ffc192c6f19ba88fdf219ee5c

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
openzeppelin-solidity	Minor

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[Amxx]

@ernestognw for the record this is usefull for the confidential tokens. They need a checkpoint structure where the "value" is a bytes32/uint256 (encrypted value pointer)