Upgrade to Svelte 5

[nstringham]

This is definitely not perfect but hopefully it's 90% of there

[ghostdevv]

Thanks for the PR! I'm not currently planning on releasing a new Svelte 5 only version of the library as I know there will be a lot of projects still on Svelte 4, and I don't want to maintain two versions of the library. In the future when Svelte 5 adoption has increased, we can hopefully release a new breaking change with only Svelte 5 support - I'll keep this around till then and we can use it as a base!

Related: #27

[nstringham]

Hopefully people update to Svelte 5 pretty quickly because they can still use most of their svelte 4 code in svelte 5 and if they really need to stay on svelte 4 they can always use an old version of your library

[nstringham]

For anyone curious, I ended up developing my own component that worked better for my use case.
https://github.com/nstringham/connexagon/blob/eca61eb7ef659434f3901650f6e8ebf11d025234/src/lib/Turnstile.svelte