fix: prevent memory leaks from uncleaned uPlot event listeners

[ahrefabhi]

Description

Fixes critical memory leaks in uPlot chart rendering that were causing memory spikes during chart re-renders and updates.

Problem

Memory profiling revealed significant memory leaks in getUplotChartOptions.ts. The function was adding multiple event listeners that were never cleaned up when charts were destroyed or re-rendered:

1. Legend tooltip listeners - mouseenter and mouseleave events on each legend item
2. Legend click handlers - Click events on markers and text elements for each series
3. Global document listener - A mousemove event listener on document that accumulated on every chart render
4. Orphaned DOM elements - Tooltip elements appended to document.body that were never removed

Each time a chart was re-rendered or updated, new event listeners were added while old ones remained attached, causing memory to grow continuously.

Solution

Implemented comprehensive event listener cleanup using uPlot's lifecycle hooks:

Changes Made

• Added tracking system: Created _legendCleanups array in ExtendedUPlot interface to track all event listeners
• Extracted inline handlers: Converted anonymous inline event handlers to named functions for proper cleanup
• Implemented destroy hook: Added destroy hook to uPlot options that removes all tracked listeners
• Enhanced component cleanup: Updated Uplot.tsx destroy callback to manually trigger all cleanup functions
• DOM cleanup: Added removal of orphaned .legend-tooltip elements from DOM

Files Modified

• frontend/src/lib/uPlotLib/getUplotChartOptions.ts - Main memory leak fixes
• frontend/src/components/Uplot/Uplot.tsx - Enhanced cleanup in React component

Impact

• Prevents memory accumulation during chart re-renders
• Eliminates memory spikes observed in profiling
• Improves overall application performance and stability
• Prevents potential browser slowdown after extended use with multiple charts

5 Heap Snapshot before Fix: (10 Sec interaction between each snapshot)

6 Heap Snapshot after Fix: (10 Sec interaction between each snapshot)

[srikanthccv]

Overall LGTM. We now have a clean up in two places 1. Uplot.tsx before chart.destroy() and hooks.destroy, please consolidate this or is there a reason to clean up in both places separately?

[srikanthccv]

This is not used.