Rebase Vite/Vitest tooling onto MSM stack (build/test only, no threadman rewrite)

[OBrezhniev]

Rebase tooling migration onto our MSM stack — build/test ONLY (Vite + Vitest)

Applies the feat/esm-migration build and test tooling on top of our
feature/msm-signed-buckets work. Target: feat/esm-migration.

Deliberately does NOT port the workerpool/threadman rewrite. Our
threadman.js (WorkerSlot + 2-phase termination) and threadman_thread.js
(batch-affine MSM second-module INIT wiring: f1m/g1m + f2m/g2m + f_conj,
GLV/GLS entry binding, Batch(NoGls|NoGlv)? fallback) plus the web-worker
dependency are kept as-is — that path carries the MSM acceleration.

• Rollup → Vite, Mocha/Chai → Vitest, flat eslint.config.js, CI.
• The Vite browser build reproduces the old rollup config exactly: bakes the
  worker thread function in as a string literal (so bundlers / monkey-patching
  frameworks can't mangle it), strips the node-only web-worker import, and
  keeps wasmbuilder/wasmcurves external (lazy).
• Tests converted in place (chai→vitest imports, before/after→beforeAll/afterAll,
  mocha timeout API → global testTimeout), preserving our GLV/GLS/batching/
  chunked-reader coverage and the SES lockdown harness (run as a child process).
• Keeps our wasmcurves git+https pin + audit overrides.

Not included: a browser Vitest project — it needs the threadman platform
split from this stack, which we intentionally didn't take. The browser build
is produced and verified.

Validation: node main.cjs + browser ESM verified; 67 tests pass incl. SES.

[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 wasmcurves#76 (full CJS→ESM; keeps our CIOS/GLV hot files)
• Rebase Vite/Vitest tooling onto MSM stack (build/test only, no threadman rewrite) #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.