Rebase ESM + Vite/Vitest onto CIOS/MSM stack

[OBrezhniev]

Rebase ESM migration onto our CIOS/MSM stack (ES modules + Vite/Vitest)

Applies the feat/esm-migration CJS→ESM conversion on top of our
feature/msm-signed-buckets work. Target: feat/esm-migration.

• CJS → ESM across src/tools/tests/index.js, Rollup-less → Vite
  (build/main.cjs for the require condition), Mocha → Vitest, flat
  eslint.config.js, CI.
• Keeps our rewritten hot files — ESM-converted in place, not replaced:
  build_f1m.js (CIOS / no-carry), build_multiexp.js (signed-digit),
  the opSub call sites in build_curve_jacobian_a0.js, the
  __reversePermutation export in build_fft.js, isKnownPrime in bigint.js
  — plus our AssemblyScript msm_batch module and its build tool.
• index.js kept as ours (no bn128_wasm_gzip export — that file isn't built).
• Interop verified: both require() and import() resolve
  { buildBn128, buildBls12381, buildF1m }.

Note: mnt6753 (legacy curve, unused by the iden3 stack) is excluded from
build:wasm and its Vitest run — its pedersen-table / base64 build tooling
needs a separate ESM pass (the same break exists on feat/esm-migration).

Validation: 87 tests pass; bn128/bls12381/msm_batch wasm regenerated.

[OBrezhniev]

ESM-rebase set — the tooling migration re-applied on top of our optimization stack (rather than replaying the branches), so the MSM/CIOS/memory work is preserved. Review together:

• Rebase ESM + Vite/Vitest onto CIOS/MSM stack #76 (full CJS→ESM; keeps our CIOS/GLV hot files)
• Rebase Vite/Vitest tooling onto MSM stack (build/test only, no threadman rewrite) ffjavascript#186 (Vite/Vitest only — WorkerSlot/batch-MSM threadman kept, no workerpool)
• Rebase Vite/Vitest tooling onto direct-io stack fastfile#137 · Rebase Vite/Vitest tooling onto our stack (keep MAX_BUFFER_SIZE fix) binfileutils#89 · Rebase Vite/Vitest tooling onto deps-update stack r1csfile#106
• Rebase Vite/Vitest tooling onto prover stack (self-contained IIFE, external bfj) snarkjs#629 (self-contained IIFE + external-lazy bfj kept)

Deviations from feat/esm-migration are called out in each PR body (e.g. binfileutils MAX_BUFFER_SIZE, snarkjs IIFE/bfj, mnt6753 excluded, smart_contracts test deferred). All branches keep git+https commit-ref pins; re-pin if a branch moves.