Scylla test changes

[ndr-ds]

Motivation

Proposal

Test Plan

Release Plan

• Nothing to do / These changes follow the usual release cycle.
• These changes should be backported to the latest devnet branch, then
  • be released in a new SDK,
  • be released in a validator hotfix.
• These changes should be backported to the latest testnet branch, then
  • be released in a new SDK,
  • be released in a validator hotfix.
• Backporting is not possible but we may want to deploy a new devnet and release a new
  SDK soon.

Links

• reviewer checklist

[ndr-ds]

Warning

This pull request is not mergeable via GitHub because a downstack PR is open. Once all requirements are satisfied, merge this PR as a stack on Graphite.
Learn more

• Scylla test changes #4198 👈 (View in Graphite)
• New ScyllaDB key space partitioning #4049
• Optimize ScyllaDB's batch writes #4047
• Some code cleanups #4066
• main

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