Make randomized simulation deterministic from a given seed

[ValarDragon]

REBASE ONTO DEVELOP ONCE SLASHING-SIMULATION IS MERGED
(Lets please merge that first, with CI disabled.)
No pending entry required, randomized testing is new to this release

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For Admin Use:

• Added appropriate labels to PR (ex. wip, ready-for-review, docs)
• Reviewers Assigned
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[cwgoes]

utACK, thanks @ValarDragon!