[Feature Request] Add introductoryOffer.subscriptionPeriod fields (NumberOfUnits, Unit) to SKProductDiscount in Unity SDK

[NikitaAver]

Feature Request

Currently the Unity Apphud.Unity.Domain.SKProduct model does not expose trial period data (introductoryOffer.subscriptionPeriod) from StoreKit configuration.

In the .storekit configuration file, each subscription has an introductoryOffer object that looks like this:

"introductoryOffer": {
  "internalID": "71B8DE8F",
  "paymentMode": "free",
  "subscriptionPeriod": "P3D"
}

However, in the Unity SDK the SKProduct and SKProductDiscount models only include:

public sealed class SKProductDiscount
{
   [JsonProperty("price")]
   [Preserve]
   public decimal Price { get; private set; }

   [JsonProperty("priceLocale")]
   [Preserve]
    public Locale PriceLocale { get; private set; }
}

This means that trial duration (e.g., 3 days) are not accessible in Unity.

Proposed Solution

Please extend SKProductDiscount to include the subscriptionPeriod data (similar to SKProductSubscriptionPeriod):

public sealed class SKProductDiscount {
    public decimal Price { get; private set; }
    public Locale PriceLocale { get; private set; }

    public int NumberOfUnits { get; private set; }
    public int Unit { get; private set; }
}