Add async offering APIs alternative (preloading all and deprecating)

[vegaro]

Motivation

With multipage paywalls we are moving the fetch of the paywall components to a separate /workflow/{offeringId} fetch per offering. Without the changes in this PR, upgrading the SDK would introduce a loading spinner on every paywall, since the paywall wouldn't be preloaded. That is a behavior change for all developers, not just those using multipage paywalls.

Description

• getOfferings() now blocks until all workflow fetches complete in parallel before firing its callback. Existing developer contract is preserved: by the time the callback fires, paywall data is ready. Failures are best-effort, a failed workflow fetch doesn't block getOfferings(), it just means that offering may show a spinner if presented.
• New async APIs for developers who want explicit control:
  • getCurrentOfferingWith(onError, onSuccess) / getOfferingWith(id, onError, onSuccess)
  • awaitCurrentOffering() / awaitOffering(id)
• Offerings.current deprecated in favor of the new APIs. getOfferings() KDoc points to them.

Next major: getOfferings() stops blocking on workflow fetches; the new APIs become the only guaranteed-no-spinner path.

Usage

No changes needed for most developers. getOfferings() works as before — paywall data is ready by the time the callback fires.

Purchases.sharedInstance.getOfferings(object : ReceiveOfferingsCallback {
    override fun onReceived(offerings: Offerings) {
        // paywall data already loaded — no spinner
        showPaywall(offerings.current)
    }
    override fun onError(error: PurchasesError) { ... }
})

New: fetch a single offering directly. Use the new APIs when you want to navigate to a specific offering's paywall without going through the full Offerings object:

// Callback
Purchases.sharedInstance.getCurrentOfferingWith(
    onError = { error -> ... },
    onSuccess = { offering -> showPaywall(offering) },
)

Purchases.sharedInstance.getOfferingWith(
    id = "premium",
    onError = { error -> ... },
    onSuccess = { offering -> showPaywall(offering) },
)

// Coroutines
val offering = Purchases.sharedInstance.awaitCurrentOffering()
val offering = Purchases.sharedInstance.awaitOffering("premium")

Deprecated: Offerings.current. Accessing it directly still works but will show a deprecation warning. Migrate to the new APIs:

// Before
Purchases.sharedInstance.getOfferings(object : ReceiveOfferingsCallback {
    override fun onReceived(offerings: Offerings) {
        val current = offerings.current // ⚠️ deprecated
    }
    override fun onError(error: PurchasesError) { ... }
})

// After
Purchases.sharedInstance.getCurrentOfferingWith(
    onError = { error -> ... },
    onSuccess = { offering -> ... },
)

[RevenueCat-Danger-Bot]

	1 Error
🚫	PR has label "feat:PaywallV2" but is missing required label(s): "pr:RevenueCatUI".

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