[core] Remove Suspense and clock mocking from regressions and e2e tests

[DiegoAndai]

Closes: #44920

Changes:

• Remove Suspense from the TestViewer component in regressions and e2e tests. They're not required and add a 300ms throttle in React 19 ([React 19] Suspense throttling behavior (FALLBACK_THROTTLE_MS) kicks in too often facebook/react#31819)
• Remove clock mocking as suggested by @Janpot

[mui-bot]

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[DiegoAndai]

The latest run indicates this is related to changes in Suspense. When removing the Suspense barrier, the regression test goes back to ~4m runtime.

[DiegoAndai]

About the broken Argos test:

• I reviewed the screenshots before the React 19 bump and they had 2014, not 2025. This is very weird to me, the year comes from {new Date().getFullYear()} (example). Do you know how were we getting 2014 before @Janpot?
• Seems like the progress bar is still flaky, so we'll probably need [docs-infra] Disable flaky demos for visual regression test #44961 or [code-infra] Stabilize flaky pigment progressbar tests #44969 anyway

On another note: Should we also remove Suspense from the e2e TestViewer?

material-ui/test/e2e/TestViewer.js

Line 16 in 4fd86d9

<React.Suspense fallback={<div aria-busy />}>

This test doesn't present such a difference (React 18 28s and React 19 36s in #44868), but it might be due to it only having 11 tests.

[DiegoAndai]

I reviewed the screenshots before the React 19 bump and they had 2014, not 2025. This is very weird to me, the year comes from {new Date().getFullYear()} (example). Do you know how were we getting 2014 before Janpot?

Answer: We're mocking the clock:

material-ui/test/regressions/TestViewer.js

Lines 35 to 38 in 4fd86d9

	const clock = useFakeTimers({
	now: new Date('Mon Aug 18 14:11:54 2014 -0500'),
	toFake: ['Date'],
	});

[DiegoAndai]

Should we also remove Suspense from the e2e TestViewer?

Confirmed that the e2e tests also shows the 300s throttling, removing

[DiegoAndai]

Ok, ready for review @Janpot

[Janpot]

Ok for me, we could live with the yearly flakey test. Alternatively, the following may work in the screenshot call to mask the copyright text:

mask: page.getByText(/Copyright © Sitemark \d\d\d\d\./)