feat: add scrollable code blocks and tables with auto-scroll during streaming

[sleitor]

Fixes #442

Summary

Adds codeBlockMaxHeight (default: 400px) and tableMaxHeight (default: 300px) props to constrain long code blocks and tables with vertical scrolling.

During streaming (isAnimating={true}), containers auto-scroll to the bottom as new content appears. If the user scrolls up to read earlier content, auto-scroll pauses and re-engages only when the user scrolls back to the bottom.

Changes

• Added codeBlockMaxHeight and tableMaxHeight props to <Streamdown>
• Code block body: max-height + overflow-y-auto + auto-scroll during streaming
• Table: max-height on inner scroll div + auto-scroll during streaming
• Auto-scroll uses passive scroll listeners and instant scrollTo for performance
• Props accept number (px) or string (any CSS value like '50vh')
• Set to 0 or Infinity to disable

Testing

• Added tests for scroll behavior, auto-scroll pin/unpin, and prop threading

[vercel]

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[vercel]

Table auto-scroll useEffect dependency array missing children, so scroll-to-bottom only fires once when streaming begins, not when new rows arrive.

[vercel]

Auto-scroll useEffect in CodeBlockBody and Table components has incomplete dependency arrays, causing scroll-to-bottom to only fire once during streaming instead of on each content update.