Memory leaks in BigTextDisplay component

[harperreed]

Problem

The BigTextDisplay.tsx component has several potential memory leaks and cleanup issues:

• Multiple useEffect hooks that create timers and event listeners don't properly clean up in all code paths
• The debouncedCalculate function creates closures over previous state values leading to stale references
• AbortController signals aren't properly checked before performing certain operations

Impact

This can lead to performance degradation, especially when navigating between screens.

Acceptance Criteria

• All useEffect hooks properly clean up timers and event listeners
• Fix stale closure issues in debouncedCalculate function
• Ensure AbortController signals are checked before operations
• Add memory leak prevention measures

Priority

High - affects app performance and user experience