fix: apply response delay conditionally

[kettanaito]

• Fixes No response when using jest.useFakeTimers() with axios and msw #966
• Extracted from feat: send mocked response body as ReadableStream to the worker #1288

Changes

• Removes setTimeout from the handleRequest so that response lookup is not concerned with actually applying a response (delaying it is, in fact, a part of applying it).
• Manually delays mocked responses in Node.js only if delay has been set.
• Adds a new integration test for ctx.delaty in Node.js.

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[kettanaito]

As responses are not always delayed now (previously always delayed by either 0 or custom delay duration), I'd expect the fake timers in Jest to work fine with MSW now:

• Not using delay: no need to advance the fake timer, response is instantaneous.
• Using delay: advance the timer by the delay duration, that should work.

[kettanaito]

Released: v0.42.3 🎉

This has been released in v0.42.3!

• 📄 Release notes
• 📦 npm package

Make sure to always update to the latest version (npm i msw@latest) to get the newest features and bug fixes.

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