feat(paint-editor): allow zoom while drawing

[saif-ellafi]

Description

Hello,

This PR is to allow navigating the paint editor while a drawing tool is active. This has been AI-assisted, but I tested myself.

Pinch, trackpad, and mouse-wheel still move the view; primary click-drag still draws. Secondary and middle mouse buttons pan, matching the main editor. An in-progress stroke is discarded if the view moves so path coordinates stay in one transform space.

Disable with PaintEditorConfigs.enableZoomWhileDrawing: false (also restores every mouse button drawing).

By default, the library behaves like it was before this PR. Flag needs to be set to true to benefit from this.

Implementation:

• Drawing already used a Listener on the canvas (that was upstream, for stylus latency). We only skip secondary/middle there when zoom-while-drawing is on.
• Right/middle pan is a Listener on the viewer (onPointerDown / Move / Up), because GestureDetector pan is tied to left-drag (panEnabled).
• Pinch, trackpad, wheel still go through the viewer’s existing GestureDetector / pointer-signal path, with scale enabled independently of pan.

Type of Change

• ✨ New feature (non-breaking change which adds functionality)
• 🛠️ Bug fix (non-breaking change which fixes an issue)
• ❌ Breaking change (fix or feature that would cause existing functionality to change)
• 🧹 Code refactor
• ✅ Build configuration change
• 📝 Documentation
• 🗑️ Chore