fix: remove side-effect from runWithRealTimers

[ph-fritsche]

What:

Rewritten runWithRealTimers and the related tests.

Why:

runWithRealTimers activated fake timers when a jest.useFakeTimers('modern') has been used in any test before.
The tests leaked setTimeout.

See #884 and #886

How:

Call jest.useRealTimers and check if any timer functions changed to determine if fake timers have been active.

Checklist:

• N/A Documentation added to the
  docs site
• Tests
• N/A Typescript definitions updated
• Ready to be merged

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[codecov]

Codecov Report

Merging #887 (97f90cc) into master (5bc9364) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master      #887   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           26        26           
  Lines          951       941   -10     
  Branches       288       283    -5     
=========================================
- Hits           951       941   -10     

Impacted Files	Coverage Δ
src/helpers.js	100.00% <100.00%> (ø)

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[eps1lon]

Going to test this build on Material-UI first so that we have a integration test with non-jest setups.

PR: mui/material-ui#25008
CircleCI workflow (test_unit failure is unrelated): https://app.circleci.com/pipelines/github/mui-org/material-ui/38295/workflows/99cb2dd3-85be-4160-bd02-4243e1a353bc

[eps1lon]

LGTM: #887 (comment)

[eps1lon]

@all-contributors add @ph-fritsche for code

@ph-fritsche Thanks!

[allcontributors]

@eps1lon

I've put up a pull request to add @ph-fritsche! 🎉

[github-actions]

🎉 This PR is included in version 7.29.5 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

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