feat: add scaleSmoothing option for smoother pinch-zoom gestures

[enhancer13]

PR Checklist

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• I have run npm test against my changes and tests pass.
• I have added tests to prove my fix is effective or my feature works. This can be done in the form of unit tests in test/unit/ or a new or altered demo in demo/.
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Description

This PR introduces a new scaleSmoothing option to address visual instability during rapid pinch-zoom gestures on mobile devices.

Problem: Fast pinch gestures on touchscreens caused trembling/jittering due to immediate scale changes between gesture events. Existing animation options weren't suitable for real-time gesture handling.

  { scale: 1.253061, positions: [100,100,150,100] }, // +25.3%
  { scale: 1.175761, positions: [100,100,145,100] }, // -6.2%
  { scale: 0.947083, positions: [100,100,130,100] }, // -24.3% 
  { scale: 1.055873, positions: [100,100,140,100] }, // +11.5%
  { scale: 0.990737, positions: [100,100,135,100] }  // -6.5%

Solution:

• Implement frame blending using smoothing factor (0-1)
• scaleSmoothing: 0 - Immediate scale changes (existing behavior)
• scaleSmoothing: 0.5 - Blends 50% of new scale with 50% previous scale