Repin mature OSS benchmark cohort to pre-2025 refs

[benvinegar]

Summary

• replace ni with zustand in the benchmark set and add payload as another mature OSS baseline
• repin every mature OSS repo to the latest default-branch commit on or before 2025-01-01
• regenerate the benchmark snapshot, report, and README summary to reflect the new baseline
• add a short note explaining the pre-2025 cutoff rationale in the benchmark docs/report

Validation

• bun run benchmark:update
• bun run format:check
• bun run lint
• bun test
• bun run build

This PR description was generated by Pi using GPT-5