Rework serialize into a compact, stable, human-readable format

Rework serialize into a compact, stable, human-readable format: a task in MiMo-V2.6-RL-harbor-code: MiMo-V2.6-RL Code (Harbor) (Harbor dataset). Our serialize(input) helper (exported from the package root) turns any JavaScript value into a deterministic string that everything else — hash , isEqual…