Svelte 5 support

Describe the bug

It's working fine in Svelte 4. I'm currently trying out the library in Svelte 5 and found my use case doesn't work.
I got an empty table with the same code. I suspect it cannot keep track of the initial element binding of the scroll element, because it works if I manually make a mounted state and call $virtualizer._willUpdate().

Your minimal, reproducible example

https://www.sveltelab.dev/github.com/rayrw/svelte5-tanstack-virtual

Steps to reproduce

I've made a minimal reproduction repo.
Please note that we have to manually run npm i --force && npm run dev before #863 is merged.
With the hack from L19-L27, it seems to work. However, when I commented out it, I got an empty table.
I suspect it cannot keep track of the initial element binding of the scroll element?

Expected behavior

I hope we can get rid of the manual mounting/element binding check and call of $virtualizer._willUpdate().

How often does this bug happen?

None

Screenshots or Videos

No response

Platform

macOS, Arc browser Version 1.65.0 (54911)
Chromium Engine Version 130.0.6723.59

tanstack-virtual version

3.10.8

TypeScript version

No response

Additional context

No response

Terms & Code of Conduct

• I agree to follow this project's Code of Conduct
• I understand that if my bug cannot be reliable reproduced in a debuggable environment, it will probably not be fixed and this issue may even be closed.

Start with the linked Svelte 5 minimal reproduction and run npm i --force && npm run dev; inspect the workaround in L19-L27 and the use of $virtualizer._willUpdate(). Compare the behavior with and without the manual mounting and element-binding check, and consider the issue resolved when the table renders in Svelte 5 without that workaround.