[Sub-Issue] Implement FlixelCheckBox and FlixelRadioButton

[stringdotjar]

Binary and mutually exclusive selection components.

Requirements (CheckBox):

• Allow developers to provide custom textures for "Checked", "Unchecked", and "Indeterminate" states.
• Toggle signal: onToggle(boolean checked).

Requirements (RadioButton):

• FlixelRadioGroup manager to ensure only one button is active at a time.
• Support for custom graphics.