Support Liquid Glass effect

[Cheesebaron]

✨ What kind of change does this PR introduce? (Bug fix, feature, docs update...)

Feature

🆕 What is the new behavior (if this is a feature change)?

This PR adds support for supplying a UIVisualEffect for the background of the Hud.

The UIToolbar view we previously used, started behaving weirdly on iOS 26.0 especially when UIDesignRequiresCompatibility was set in Info.plist, since it now doesn't support background colors the same way.

So instead of using UIToolbar for a subtle background blur effect, I decided just allowing the developer to supply their desired effect instead, when not setting a visual effect, it uses a background color.

So on iOS/maccatalyst 26.0 and up we now default to Liquid Glass appearance set by:

• BackgroundVisualEffect defaulting to UIGlassEffectStyle.Regular
• HudBorderThickness defaulting to 1pt
• HudBorderColor defaulting to UIColor.White
• HudCornerRadius defaulting to 20pt

The first 3 properties are new on ProgressHUDAppearance and can be overridden by the developer.

💥 Does this PR introduce a breaking change?

If you use BackgroundVisualEffect the HudBackgroundColor is now ignored, so this only works when BackgroundVisualEffect is set to null

🐛 Recommendations for testing

A few screenshots of the new effect

📝 Links to relevant issues/docs

Fixes #124

🤔 Checklist before submitting

• All projects build
• Follows style guide lines
• Relevant documentation was updated