Create PaywallPurchaseContext to PurchaseLogic for product changes and offers

[vegaro]

This is a followup from #3062 (comment)

• Introduces PaywallPurchaseLogic and PaywallPurchaseLogicWithCallback. New interfaces extending the existing PurchaseLogic/PurchaseLogicWithCallback, enabling developers using MY_APP mode to handle subscription upgrades/downgrades and promotional offers from paywalls.
• New implementations receive a PaywallPurchaseContext containing the package, an optional ProductChange, and an optional SubscriptionOption.
• Deprecates PurchaseLogic and PurchaseLogicWithCallback in favor of the new interfaces. Existing implementations continue to work without changes.
• Developers adopting PaywallPurchaseLogic only need to implement performPurchase(activity, context). No need to implement the old performPurchase(activity, rcPackage).

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Note

Medium Risk
Touches purchase execution paths for MY_APP mode and changes public API types, so regressions could break custom purchase integrations despite deprecation shims and added tests.

Overview
Adds a new custom purchase API for paywalls: PaywallPurchaseLogic (plus PaywallPurchaseLogicWithCallback) and a PaywallPurchaseLogicParams object that carries the Package plus optional product-change (oldProductId/ReplacementMode) and SubscriptionOption offer details.

Updates all paywall entry points (PaywallOptions, PaywallDialogOptions, PaywallActivityLaunchOptions, PaywallView) to accept PaywallPurchaseLogic instead of PurchaseLogic, and deprecates the old PurchaseLogic/PurchaseLogicWithCallback while keeping them source-compatible via an adapter implementation.

Wires the new params through PaywallViewModel when PurchasesAreCompletedBy.MY_APP, and expands tests + api-tester coverage to validate the new context is passed for product changes and resolved offers; public API surface (api.txt) is updated accordingly.

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[tonidero]

Some thoughts on the API. Not ideal to have 2 such similarly named types... but I think it might be the better option so let's go with this.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 79.22%. Comparing base (992bf06) to head (c2e5fa7).

Additional details and impacted files

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  Files         347      347           
  Lines       13911    13911           
  Branches     1884     1884           
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  Hits        11021    11021           
  Misses       2109     2109           
  Partials      781      781           

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[cursor]

Cursor Bugbot has reviewed your changes and found 1 potential issue.

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[tonidero]

Nice one! I think this is probably the cleanest 🫶
I guess we need to do similar changes in iOS + hybrids right? One step at a time 😅