Add Svelte 5 support via /svelte subpath export

[MathiasWP]

Summary

Adds Svelte 5 as a first-class adapter alongside the existing React one, via the subpath export @itsmeadarsh/warper/svelte. The Svelte build does not pull React into its import graph — both react and svelte are now optional peer deps.

• New exports: createVirtualizer (rune-based hook) + <Warper> .svelte component, mirroring the React hook + component surface.
• Shared core: the zero-allocation TypedArray buffer pools were extracted out of react/hooks/useVirtualizer.ts into core/buffers.ts so both adapters reuse the same hot-path scratch space.
• Types split: types/core.ts is framework-agnostic; types/react.ts holds the React-only types. types/index.ts re-exports both, so existing React imports are unchanged.
• Build: new build:svelte script runs @sveltejs/package with a dedicated tsconfig.svelte.json, emitting dist/svelte/ with .svelte.d.ts types.
• .svelte-kit/ (scratch dir from svelte-package) is gitignored.

Idiomatic Svelte 5 choices (verified against svelte.dev docs)

• $state.raw for the range object — TypedArray-backed views are reassigned wholesale, so deep proxy reactivity would be pure overhead.
• @attach attachments (Svelte 5.29+) instead of use: actions for the scroll container.
• on() from svelte/events for the scroll listener.
• style: directives for dynamic style values (height / transform); static styles stay in a single style attribute.
• Typed Snippet<[number]> children; {@render children(itemIndex)}.
• Plain $effect for lifecycle (consumers needing non-component usage can wrap in $effect.root).

Test plan

• bun install succeeds; no React-related warnings in a Svelte-only consumer environment.
• bun run build produces dist/svelte/index.js, components/Warper.svelte, hooks/createVirtualizer.svelte.js plus matching .d.ts files.
• React entrypoint (@itsmeadarsh/warper) still builds and the existing examples (bun run example:list etc.) still run.
• Smoke test in a SvelteKit / Vite-Svelte playground: import { Warper, createVirtualizer } from @itsmeadarsh/warper/svelte, render 1M rows, verify scroll, range.items updates, scrollToIndex works.

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