fix(group): after a sequence of updates a proof is invalid

[Lauman]

Description

When a member is removed from the group (update a leaf with 0n) and then another member is updated, the root that is saved is not correct, so the proof that is generated is not valid.
This bug is fixed by updating the lean-imt library, which was recently updated.
I detected this when I was testing the script create-mock-groups.

Other information

The fix
privacy-scaling-explorations/zk-kit#355

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• My changes generate no new warnings
• I have run yarn format and yarn lint without getting any errors
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

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