kerosene: Fix waitForEventLoopToDrain breaking in Jest

[nhardy]

Was previously thinking about using package.json exports to define something different for Node and the browser, but jest-environment-jsdom now uses the browser resolution for packages which rendered that approach no longer viable.

Instead, we can check for the presence of jest.requireActual if globalThis.setImmediate is not available to determine if we're in a jest environment, and require the actual, unstubbed Node timers module. Thankfully, unlike require, jest.requireActual should be ignored by bundlers like esbuild, webpack and rollup and should not result in Node requires in code that is intended for browsers.

[coveralls]

Coverage decreased (-0.4%) to 76.079% when pulling 25b9315 on bugfix/kerosene-waitForEventLoopToDrain-jest into e6f1b94 on master.

[Priddles]

Nice find!