Add standalone Apple Pay button support in Stripe payment form

[Khalid2Faisal]

This PR adds support for using Apple Pay as a standalone payment option in the Stripe payment form. The implementation includes:

Key changes

• Added a dedicated Apple Pay button that appears when Apple Pay is available
• Added cancel event handler to reset button state when user closes Apple Pay sheet
• Implemented direct callback approach with onApplePayAvailable to notify when Apple Pay is available

New configuration options

The PR introduces new configuration options in PaymentProviderFormOptions.applePayConfig:

• priceMacro: Specifies which price macro to use from the product bundle properties (defaults to "new-price")
• productMacro: Specifies which product macro to use for product name from the bundle properties
• productLabel: Directly set the product label shown on Apple Pay sheet
• staticPrice: Alternative to using bundle properties - directly set price details:
  -- currency: Currency code (e.g., "usd")
  -- amount: Price amount in cents
• requestPayerName, requestPayerEmail, requestPayerPhone: Configure what information to request
• onApplePayAvailable: Callback function triggered when Apple Pay is available
• showApplePayInPaymentElement: Control visibility of Apple Pay in the payment element (used with default stripe form)

Usage Example

apphud.paymentForm({
    id,
    paymentProvider: "stripe",
    applePay: true,
    applePayConfig: {
        // Use price from product bundle with specified macro
        priceMacro: "new-price",
        
        // Use product name from bundle with specified macro
        productMacro: "custom-1",
        
        // OR directly set the product label
        productLabel: "Premium Subscription",
        
        // OR use static price directly
        staticPrice: {
            currency: "usd",
            amount: 999, // $9.99
        },
        
        // Additional configuration
        requestPayerName?: true;
        requestPayerEmail?: true;
        requestPayerPhone?: false;
        onApplePayAvailable: (isAvailable) => {
            console.log("Apple Pay available:", isAvailable);
        }
    }
})