Update to svelte 5

[jdtjenkins]

Changes

Updates the @astrojs/svelte integration to use Svelte 5 by default. This change is necessary because the Svelte 5 Vite plugin only supports Svelte 5 and has dropped all v4 support. So it'd be really messy supporting both versions in one integration. We'd be better off cutting a new major and only supporting v5 on the new major and beyond.

Removes all Svelte 4 code and deps from the integration.

Fixes or updates all the tests to use Svelte 5 components.

Testing

All the unit tests have been updated to use the newer Svelte 5 syntax, all the fixtures have also been updated to use Svelte 5 as a dependency. Running the fixtures shows the integration works and loads up Svelte 5 components.

Docs

I... Should add some docs for this yes. This will be a pretty big change(? or a reasonably sized one I guess) as we'll now stick Svelte 4 on a certain major of the package, and carrying on will only be Svelte 5 support.

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Latest commit: 1bab62d

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