Smooth package-list scrolling and stop re-parsing SVG icons on every scroll

[Gabriel Dufresne (GabrielDuf)]

This pull request introduces two main improvements: smoother DataGrid wheel scrolling and significant performance optimization for SVG icon loading. The new DataGridWheelAnimator class provides a WinUI-like eased scroll experience, and the SvgIcon control now memoizes parsed SVGs to avoid redundant parsing and asset loading, greatly improving UI responsiveness during heavy DataGrid usage.

UI/UX Improvements:

• Added DataGridWheelAnimator to enable eased, animated wheel scrolling for DataGrid, replacing the default instant jump with a smoother experience. This is achieved by driving the internal scroll method via reflection and gradually applying the scroll delta. (src/UniGetUI.Avalonia/Views/Controls/DataGridWheelAnimator.cs, src/UniGetUI.Avalonia/Views/Controls/DataGridWheelAnimator.csR1-R65)
• Integrated the new scroll animator by attaching it to PackageList in the packages page, so users benefit from the improved scrolling immediately. (src/UniGetUI.Avalonia/Views/SoftwarePages/AbstractPackagesPage.axaml.cs

Performance Optimizations:

• Refactored SvgIcon to cache parsed SVGs using a thread-safe dictionary, preventing repeated parsing and asset loading for the same icon URI. This greatly reduces UI thread work and improves scrolling performance when icons are reused. (src/UniGetUI.Avalonia/Views/Controls/SvgIcon.cs
• Moved SVG parsing logic into a static method and record, ensuring that geometry and viewbox calculations are performed once per unique asset and reused efficiently. (src/UniGetUI.Avalonia/Views/Controls/SvgIcon.cs