Add svelte signal configuration package

[jacojoubert]

If this PR updates API docs, preview them by:

• install bun (if needed)
• install volta and configure it for pnpm (if needed)
• run pnpm install in the root (if needed)
• run pnpm preview in the root

---

• Read the full contributing documentation
• If you do not have permission to add labels or run the test-suite in CI, a team member will do this for you.

[runspired]

generally this seems like the right approach. We'll still want to implement the Request component, though with svelte having unfortunately deprecated?(demoted?) its slots API it may be more ergonomic to just use a RequestSubscription directly in svelte.

I'll get this rebased and bring it up to speed with the isolated-declarations work over the coming week.

[jacojoubert]

@runspired What blocks us from using snippets? They dropped slots because they dropped web component support. As far as I know there isn't any downside to snippets? I can build out the request component.

[jacojoubert]

I am out for a week, but when I get back I will add a few more tests some, helper components, and get this over the line.

[runspired]

What blocks us from using snippets? They dropped slots because they dropped web component support. As far as I know there isn't any downside to snippets? I can build out the request component.

The trouble with snippets is just the verbosity and the inverted control flow. By the time someone wires them up they may as well have just written their own if/else using the reactive SubscriptionState class directly. Reminds me of all the worst parts of contextual components in ember.