fix: ship csv-parse stream cjs export

[YfengJ]

Summary

csv-parse declares a CommonJS export target for csv-parse/stream:

"./stream": {
  "require": {
    "types": "./dist/cjs/stream.d.cts",
    "default": "./dist/cjs/stream.cjs"
  }
}

However, the package currently ships only index and sync files under dist/cjs, so CommonJS consumers hit MODULE_NOT_FOUND when using require("csv-parse/stream").

This PR makes the declared CommonJS stream subpath real by:

• adding a Rollup CJS build for lib/stream.js
• copying lib/stream.d.ts to dist/cjs/stream.d.cts during build:ts
• adding a regression test that loads the exact exports["./stream"].require.default target from package.json

Runtime source code and public API behavior are unchanged; this aligns the published files with the package export map.

Validation

• Watched the new regression test fail before the fix with missing dist/cjs/stream.cjs
• npm run build
• npx mocha 'test/api.stream.cjs_export.js'
• Full package test in a temporary no-space path because the existing samples test path handling breaks when the checkout path contains %20: npm test -> 608 passing, 3 pending
• npm pack --ignore-scripts --json ., verified the tarball contains:
  • package/dist/cjs/stream.cjs
  • package/dist/cjs/stream.d.cts
• Required the packed CJS stream file and verified parse is exported
• npx eslint packages/csv-parse/rollup.config.js packages/csv-parse/test/api.stream.cjs_export.js
• git diff --check

Note: the full npm run lint:check --workspace csv-parse currently fails on unrelated existing lint issues in test/api.sync.ts and test/api.web_stream.ts, plus existing pending-test warnings. The files touched by this PR pass eslint.