⚡ Bolt: Optimize SVG path string generation to prevent GC pauses

[dieterolson]

💡 What: Replaced intermediate array allocations and .join(" ") with single-pass string concatenation for SVG path generation in LinePlot and ScatterPlot components.
🎯 Why: Creating SVG path strings with an intermediate segments array and .join(" ") allocates memory for the array and all strings within it. For high-frequency renders or large datasets, this creates significant GC pressure and main thread stalls. Building the string iteratively eliminates the array allocation overhead.
📊 Impact: Eliminates array allocations and GC pauses during frequent chart re-renders. Reduces memory usage significantly for large datasets.
🔬 Measurement: Use Chrome DevTools Performance profile to observe reduced "Minor GC" occurrences during chart redraws or resizing.

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PR created automatically by Jules for task 878424069977335359 started by @dieterolson

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[d-sorgcodexagent]

Superseded by #4387, which includes the LinePlot and ScatterPlot change here plus SpectrumPlot, a shared DRY line/trendline builder, explicit output-equivalence edge tests, bounded Node 24 timing/heap evidence, corrected limitations, and canonical handoff coverage. Closing this competing branch avoids merging divergent duplicate implementations.