chore: convert @packages/net-stubbing tests to vitest from mocha

[AtofStryker]

• Closes

Additional details

converts the @packages/net-stubbing tests from mocha to vitest. Conversion was mostly 1:1

Steps to test

How has the user experience changed?

PR Tasks

• Have tests been added/updated?
• Has a PR for user-facing changes been opened in cypress-documentation?
• Have API changes been updated in the type definitions?

---

Note

Migrates @packages/net-stubbing unit tests to Vitest, updates package scripts/config, adjusts CI test-results count, and marks migration complete in docs.

• Tests (@packages/net-stubbing):
  • Convert unit tests from Mocha/Chai/Sinon to Vitest in test/unit/*.spec.ts (use describe/it/expect, vi.fn, and toEqual/toMatchObject, etc.).
  • Add Vitest config: packages/net-stubbing/vitest.config.ts (Node env, globals, includes, CYPRESS_INTERNAL_ENV=test).
• Package Configuration:
  • packages/net-stubbing/package.json:
    • Replace Mocha test script with vitest; add test-watch and test-debug.
    • Remove mocha/chai dev deps; add vitest.
• CI:
  • .circleci/src/pipeline/@pipeline.yml: reduce sanitize-verify-and-store-mocha-results.expectedResultCount from 7 to 6 in unit-tests job.
• Docs:
  • guides/esm-migration.md: mark packages/net-stubbing as ✅ completed under Phase 2.

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