Optimize grapheme renderer performance

[brandonkachen]

Summary

• replace the lodash-based grapheme diffing with lightweight helpers and direct string command generation
• cache cursor state in the renderer to avoid redundant cursor writes and skip unnecessary stdout updates
• clean up timer management with clearTimeout/clearInterval during refresh and shutdown

Testing

• pnpm --filter @codebuff/display typecheck (fails: missing grapheme-splitter module because node_modules is absent in the workspace)

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https://chatgpt.com/codex/tasks/task_e_68fc6b85e500832ca47e1231856746b2