change int to double in font size

[buihongvinh]

The app stores reader font size as a percentage for UI/persistence, but Readium Android/Web expects fontSize as a scale value. Passing 100.0 compiles but does not behave correctly; it should be sent as 1.0. iOS currently divides fontSize by 100 in the native bridge, so it still receives the percentage value. typeScale should also be updated from the same scale so the rendered text actually changes with the slider.

EPUBPreferences buildPreferences(TextSettingsState settings) {
final clampedFontSize = settings.fontSize.clamp(70, 200);
final fontScale = clampedFontSize / 100.0;

return EPUBPreferences(
// UI stores font size as percent: 70, 100, 150, 200.
// Android/Web Readium expects scale: 0.7, 1.0, 1.5, 2.0.
// iOS bridge currently divides fontSize by 100 internally.
fontSize: defaultTargetPlatform == TargetPlatform.iOS
? clampedFontSize.toDouble()
: fontScale,

// Keep typeScale in sync with the selected font size.
typeScale: fontScale,

publisherStyles: false,
fontFamily: settings.fontFamily,
lineHeight: settings.lineHeight,
letterSpacing: settings.letterSpacing,

);
}