test(prover-node): make checkpoint store pruning test deterministic

[AztecBot]

Summary

• Fixes the merge-queue failure on PR feat: merge-train/spartan-v5 #24053 by making CheckpointStore's pruning test use explicit slots for its synthetic checkpoints.
• The failed CI run was merge-group run 27616214374; CI3 job 81652669415 failed in x9-full (http://ci.aztec-labs.com/11cc1d3bfd3986cf).
• The failing test was yarn-project/scripts/run_test.sh prover-node/src/checkpoint-store.test.ts, log http://ci.aztec-labs.com/0e7cfabe067f8bed, where markPrunedAboveBlock marks every prover holding a block above the target and returns them hit the stricter same-slot canonical checkpoint guard while building random test data.

Verification

• git diff --check
• ./bootstrap.sh ci attempted, but this branch's root bootstrap has no ci target and the container has no Docker socket.
• ./bootstrap.sh ci-full-no-test-cache attempted to match the failed merge-queue leg, but local bootstrap failed before project tests because the test engine exited and interrupted the parallel build.
• Focused Yarn/Jest verification is blocked in this checkout because yarn-project portal dependencies under noir/packages/* are not generated; noir/bootstrap.sh is blocked by a crates.io DNS/proxy failure while installing just.

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Created by claudebox · group: slackbot