SelectionInputHandler.cs

It manages both single-click and drag selection of game objects, with support for:

• Single/Multiple unit selection

• Modifier keys (Shift, Ctrl) for adding/removing units

• Double-click to select similar units

• Tab cycling through unit groups

• Customizable selection priorities

• Drag box selection

Key customization points:

• Inherit this class to customize selection behavior by overriding virtual methods likeHandleClickEvent and HandleDragReleaseEvent.