fix: memo comparison functions return false instead of true

[alessandroliva]

In this PR I propose a fix for React.memo comparison functions in Messages and PreviewMessage that always returne false, effectively disabling memoization.

Problem

Both components define a custom comparison function for React.memo, but they end with an unconditional return false.
Because the final line is always false, these components re-render on every parent update, regardless of whether the relevant props actually changed.

Testing

Verified the app still updates when:

• New messages are added.
• Streaming status changes (e.g. streaming → ready).
• Votes change.
  Confirmed that, when props are unchanged, the components are now eligible to be skipped by React.memo, reducing unnecessary re-renders in longer chats.

[vercel]

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