fix(ui): auto reload coverage iframe after test run

[hi-ogawa]

Description

• Closes Coverage report should be refreshed in the UI when tests are re-run #5057

I tested a simple iframe reloading and tested by pnpm -C examples/basic test:ui --coverage:

Show demo

2024-02-20.13-35-10.webm

But actually I'm worrying that there might be some race condition here:

vitest/packages/vitest/src/node/core.ts

Lines 529 to 530 in a479115

	await this.report('onFinished', this.state.getFiles(specs), this.state.getUnhandledErrors())
	await this.reportCoverage(allTestsRun)

If reportCoverage takes significant time, then reloading iframe during onFinished might end up fetching old coverage html.

To avoid this race condition, it might be necessary to either:

• add new reporter hook (like onReportCoverageFinished) just for this, or
• move up reportCoverage before onFinished (this would likely mess up terminal output for coverage text reporter) or
• provide a dedicated "iframe reload" button on UI, so users can at least reload it manually.

I'm leaning towards the 1st option, but what do you think?

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