feature/sk2-observer-mode

[yusuftor]

Changes in this pull request

In SK2 we can't access the purchase from the transaction updates observer. Instead, we observe SK2 purchases if the app is using SK2 and if the shouldObservePurchases SuperwallOption is set to true.

The first thing that happens is we cache legacy transactions. This ensures transactions from before an SDK upgrade are cached to maintain consistency, avoiding redundant processing.

Then when the app enters the foreground it detects and processes unobserved transactions. First, this checks that there's no Superwall purchase happening. Then it checks that it gets a list of previously cached transactions to check we haven't already processed it. Then it checks the decoded jwsRepresentation paywall of the transaction to make sure it's a purchase instead of a renewal and extract whether an offer was purchased. Then we log a transaction start/complete for the given transaction.

Checklist

• All unit tests pass.
• All UI tests pass.
• Demo project builds and runs.
• I added/updated tests or detailed why my change isn't tested.
• I added an entry to the CHANGELOG.md for any breaking changes, enhancements, or bug fixes.
• I have run swiftlint in the main directory and fixed any issues.
• I have updated the SDK documentation as well as the online docs.
• I have reviewed the contributing guide