Allow onApply to accept either a synchronous or asynchronous function

[brandonmcconnell]

• Introduce MaybePromise and MaybeAsync type helpers
• Allow onApply to accept either a synchronous or asynchronous function

[stackblitz]

Run & review this pull request in StackBlitz Codeflow.

[changeset-bot]

🦋 Changeset detected

Latest commit: 7653594

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
svelte-ux	Patch

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR

[github-actions]

built with Refined Cloudflare Pages Action

⚡ Cloudflare Pages Deployment

Name	Status	Preview	Last Commit
svelte-ux	✅ Ready (View Log)	Visit Preview	7653594

[techniq]

Care to also PR this to LayerStack, which is where 99% of Svelte UX's utils, actions, stores, etc will be living going forward.

I've extracted them as separate packages, and the LayerChart will soon only have a devDependency on Svelte UX after simplified PRs merge (LayerStack will also be getting a lot of utils from LayerChart for a common location that can be used in non-Svelte UX/LayerChart/and some cases Svelte projects.

Svelte UX will be updated to use @layerstack/* packages for most/all of these, and likely re-export to reduce the breaking change until closer to 1.0 (still debating)