Tests: Upgrade dependencies, improve isolation and experience on Windows

[medikoo]

Closes #6116

• Upgrade:
  • chai from v3 to v4
  • chai-as-promised from v6 to v7
  • mock-require from v1 to v3
  • proxyquire from v1 to v2
• Fix exposed issues
• Improve home dir isolation among test runs
• Improve logic responsible for local invocations, so spawn errors are handled (they were thrown in the air as uncaught exceptions), and promise rejects with them instead of EPIPE errors (which are no longer introduced in such case)
• Ensure isolated tests run without issues on Windows
• Increase default timeout to 5000 (with 2000 on Windows VM some tests occassionally fail with timeout errors)
• Introduce skip with notice functionality. It allows us to skip test destined to fail due to our environment setup (e.g. lack of admin rights, Python not installed etc.). It's configured to be ineffective in CI, where all tests are expected to pass.
• Patch other discovered Mocha bugs
  • Uncaught exceptions are silenced if happen in timeframe of skipped test mochajs/mocha#3938
  • 🗣️ Discussion: this.skip() - bug summary mochajs/mocha#3740

Is this ready for review?: YES
Is it a breaking change?: NO

[pmuens]

This looks good! Really nice cleanup 👍

LGTM