Fix style crawling logic for CSS HMR

[bluwy]

Changes

Fix #7529

Used the not-so-performant technique initially used in the first commit of #7381 to fix the issue for now.

The issue seems to be that UnoCSS is invalidating the Astro files at https://github.com/unocss/unocss/blob/757b7f18b060f32387689545c878aea1e63203b4/packages/vite/src/modes/global/dev.ts#L59. This breaks our expectations where they are already loaded and exist as ssrTransformResult. The invalidation clears out ssrTransformResult, causing the issue.

A fix I intially thought is to force loader.import() on all modules while we're traversing the graph to counteract UnoCSS, but that feels more non-performant than the initial PR idea, so I went with the initial PR idea instead.

Testing

Existing tests should pass. Also tested the repro locally. Unfortunately time is a bit tight for me now to add a real test with unocss.

Docs

n/a.

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[duxphp]

[unocss-hmr] failed to get unocss hash, hmr might not work

The error is still reported when using unocss

[bluwy]

Can you provide a repro where that's happening?

[marvin-j97]

Can you provide a repro where that's happening?

https://stackblitz.com/edit/withastro-astro-yrtpg7?file=package.json

[bluwy]

Thanks for the repro. Seems like it's a browser warning log, not an error. And it's also happening in 2.7.0, which is out of scope of this PR as it's fixing a regression from 2.7.1.

IIUC this needs to be fix upstream at https://github.com/unocss/unocss/blob/757b7f18b060f32387689545c878aea1e63203b4/packages/vite/src/modes/global/dev.ts#L187C6-L198, skipping the warning if __vite_css__ is an empty string.