Multitouch events support

[kunitoki]

This pull request introduces comprehensive multitouch support across all platforms with touch hardware, improves the user experience for touch and mouse interactions, and adds a new example demonstrating these capabilities. The changes affect the core event system, UI documentation, and the graphics examples.

Multitouch support and event system enhancements:

• Added full multitouch support: Each finger on a touch device now generates its own set of mouse events (mouseDown, mouseDrag, mouseUp) with a stable touch index and pressure information, allowing for independent tracking of multiple fingers. Touch pressure is now accessible via MouseEvent::getPressure(), and each finger is hit-tested independently. SDL's synthetic touch-to-mouse events are disabled to prevent duplicate event delivery. (CHANGELOG.md, yup_MouseEvent.cpp) [1] [2] [3] [4] [5] [6]

UI improvements and bug fixes:

• Fixed a bug where the Slider component could remain in a hover state after a touch drag if the pointer was released outside its bounds; mouseUp now directly clears the hover state when appropriate. (CHANGELOG.md)

Documentation and examples:

• Expanded documentation to explain multitouch handling, including code samples for tracking multiple fingers and implementing gestures like pinch-to-zoom. (component-basics.md)
• Added a new "Touch Trails" example to the graphics examples, which visually demonstrates multitouch input by drawing colored trails for each finger or mouse pointer, with smooth fading and independent tracking. The example is integrated into the main demo application. (TouchTrails.h, main.cpp) [1] [2] [3]

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.61%. Comparing base (ff8ad8e) to head (88fea07).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #180      +/-   ##
==========================================
+ Coverage   81.53%   81.61%   +0.08%     
==========================================
  Files         796      796              
  Lines       82695    82713      +18     
==========================================
+ Hits        67425    67508      +83     
+ Misses      15270    15205      -65     

Files with missing lines	Coverage Δ
modules/yup_gui/mouse/yup_MouseEvent.cpp	92.63% <100.00%> (+1.27%)	⬆️
modules/yup_gui/mouse/yup_MouseEvent.h	100.00% <ø> (ø)
modules/yup_gui/widgets/yup_Slider.cpp	54.50% <100.00%> (+13.71%)	⬆️

... and 7 files with indirect coverage changes

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