enable async usage in svelte

[benoitf]

Is your enhancement related to a problem? Please describe

async usage in svelte is not really possible in $derived + markup, etc. but it could solve lot of workaround/issues being done today to make it work.

following a meeting with maintainers, we want to enable the feature.

Describe the solution you'd like

• [x] Allow its usage by enabling the compiler option of svelte to authorize this more information on https://svelte.dev/docs/svelte/await-expressions

• [ ] Add a note in contributing guide

Describe alternatives you've considered

No response

Additional context

No response