Simplify HMR for circular imports and CSS

[bluwy]

Changes

This PR removes a good portion of the HMR code with an approach that lets Vite invalidates the modules accordingly instead. The highlights are:

1. Simplify handleHotUpdate. It now only does two things: "check style-only updates" and "handle circular dep edge case" (latter can be removed in the future)
2. Simplify Astro compilation caching and invalidation.
3. Remove redundant import.meta.hot.decline() calls. They don't work in Vite.

Testing

Added a test from #9370

While this should fix it #9370, I'd like to further improve HMR more noted in the TODOs, including:

• Refactoring away Astro compilation cache. Vite already has its own cache and we can rely on that instead. (Saves on memory)
• Fine-grained CSS updates (When the Vite PR lands)

Docs

n/a. should be internal refactor and HMR will work as expected

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