Use new untrack utility function when available

[Lms24]

Currently we rely on a hacky way of accessing certain SvelteKit event properties without triggering a route invalidation in our load wrappers.

SvelteKit 2 introduced the long discussed untrack function which should allow us to access the values in a safe and SvelteKit native way without triggering invalidation.

Since we want to maintain 1.x support, we need to implement this backwards-compatible and still rely on our hacky approach until we drop 1.x sometime in the future.

[AbhiPrasad]

Is this something we can evaluate for v9?

[Lms24]

@AbhiPrasad Yes we should! Since we already discussed dropping SvelteKit 1.x support for v9, we could simply use untrack.