The fold got ~78× faster, and proves it changed nothing

lidapters gains a config-selected incremental state-fold strategy alongside the default full-rebuild path, a whole-strategy swap chosen once at construction.

• Two strategies, one contract: a stateless reference reducer and a persistent incremental builder, producing byte-identical output.
• Measured over 20,000 real mainnet ledgers: roughly 78× faster fold-only at real state size, with identical checksums.
• A parity gate fails loudly if the two strategies ever drift apart.