Add Properties: headerRowHeight & rowsPerPage

[gzimbron]

🎯 Changes

@gzim/svelte-datagrid:

• Add Properties: headerRowHeight & rowsPerPage
• Fix: Negative Y scroll on iOS blink

Website:

• Add controls to show state, and scroll to specific row index

✅ Checklist

• [x] I have given my PR a descriptive title
• [x] I have run pnpm run lint locally on my changes
• [x] I have run pnpm run test locally on my changes