fix(data-testing): mark conformance-case calls @__PURE__ so unused fixtures tree-shake

[krisnye]

Summary

• An unused co-located cases export (export const cases = Conformance.cases(fn, ...)) is not eliminated from a production bundle just because @adobe/data-testing's package.json sets sideEffects: false — that flag only lets a bundler drop an unused import of the package. Conformance.cases(fn, ...) / Conformance.derivations(fn, ...) is an ordinary, unannotated function call happening in the consuming transform file, so Rollup/esbuild conservatively keeps it whenever the module is reachable (i.e. whenever fn itself is genuinely used), even though the cases export it initializes is never read.
• Verified empirically against a real Vite/Rollup production build (data-lit-todo): wiring a transition into the actual app entry point and calling only the function (never cases) shipped the full case-fixture data and the builder's inlined logic into the bundle. Adding /*@__PURE__*/ immediately before the call eliminated it completely, confirmed by rebuild.
• Annotates all 34 existing Conformance.cases(...) / Conformance.derivations(...) call sites across the reference apps (data-lit-todo, data-lit-tictactoe, data-gpu-hopper, data-lit-space-rock-game, data-react-pixie), corrects the misleading sideEffects: false comment in packages/data-testing/src/index.ts, and updates the data-ai guidance (state.md) to require the annotation on every future call, with the mechanism explained so it isn't dropped by accident.
• Standard pnpm -w run bump version bump included per workspace convention.

Test plan

• pnpm run lint — passes
• pnpm run typecheck — passes across all 18 workspace packages
• pnpm --filter <touched-app> run test — all pass (data-lit-todo 106/106, data-lit-tictactoe 99/99, data-lit-space-rock-game 135/135, data-gpu-hopper 90/90, data-react-pixie 42/42, data-testing 18/18)
• Re-ran the real Vite production build after the fix to confirm no regression in bundle output

🤖 Generated with Claude Code