feat: add content debouncing to ReasoningBlock for improved streaming performance

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Summary

This PR builds upon PR #8000 by adding content debouncing to the ReasoningBlock component, addressing the suggestion from @hannesrudolph about capping the maximum number of renders per second during content streaming.

Problem

While PR #8000 fixed the timer-related performance regression, rapid content streaming (especially with fast models like Claude) could still trigger many re-renders as content updates arrive.

Solution

This implementation adds a debouncing mechanism for content updates during streaming:

1. Content Debouncing:

   • Implements a 100ms debounce for content updates during streaming
   • Caps maximum renders to ~10 per second
   • Immediately updates when streaming completes to show final content without delay

2. Combined with Timer Isolation (from PR fix: optimize ReasoningBlock performance by isolating timer re-renders #8000):

   • Memoized ElapsedTime component prevents timer updates from triggering parent re-renders
   • Timer updates remain isolated at 1Hz

Changes

• Added debouncedContent state to track debounced content separately
• Implemented updateDebouncedContent using the existing debounce package (100ms delay)
• Content updates are debounced during streaming but immediate when streaming completes
• Proper cleanup of debounce timers on unmount

Testing

• ✅ All existing tests pass
• ✅ TypeScript checks pass
• ✅ Linting passes
• ✅ Manual testing confirms improved performance during rapid streaming

Performance Impact

• Before: Content updates could trigger re-renders as fast as the stream provides data
• After: Content re-renders are capped at ~10 per second during streaming, significantly reducing CPU usage

This addresses the performance concerns raised in #7999 and implements the suggestion from the issue discussion.

cc @hannesrudolph @nabilfreeman

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Important

Adds content debouncing to ReasoningBlock to limit re-renders during streaming, improving performance.

• Behavior:
  • Adds 100ms debounce to ReasoningBlock content updates during streaming, capping renders at ~10 per second.
  • Immediate content update when streaming completes.
• Components:
  • Memoizes ElapsedTime to prevent full ReasoningBlock re-renders every second.
• State Management:
  • Introduces debouncedContent state in ReasoningBlock.
  • Uses debounce package for content update debouncing.
  • Cleans up debounce timers on unmount.
• Performance:
  • Reduces CPU usage by limiting re-renders during rapid content streaming.

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Reviewing my own code is like debugging in a mirror - everything looks backwards but the bugs are still mine.

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Since this is a performance-critical component with complex debouncing logic, it would benefit from test coverage. Consider adding tests to verify:

• The 100ms debouncing behavior works correctly
• Content updates immediately when streaming stops
• The ElapsedTime component properly isolates re-renders
• Cleanup happens on unmount

[roomote]

The comment mentions "~10 per second" but with a 100ms debounce, it's exactly 10 per second maximum. Consider updating for precision:

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Is it intentional that the debounce delay is hardcoded to 100ms? Consider making this configurable via props for different use cases, or at least extracting it as a named constant for better maintainability.

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Good edge case handling here - immediately updating content and clearing pending debounces when streaming stops. This ensures the final content is shown without delay. Though if streaming rapidly toggles between true/false, could there be any race conditions? The implementation looks correct, but might be worth documenting this behavior.

[roomote]

Closing this PR as requested. The debouncing changes will be applied to PR #8000 instead.