[RN][Bug]: Forward accelerated checkout dismissal callbacks

[kieran-osgood-shopify]

What changes are you making?

Forward accelerated checkout lifecycle events from every presentation layer to the existing EventHandlers callbacks.

• Pass the accelerated checkout controller as the CheckoutDelegate when Shop Pay or Apple Pay presents Checkout Kit.
• Forward Checkout Kit dismissal and terminal failure events from Shop Pay and Apple Pay.
• Report checkoutDidDismiss when the buyer closes the native Apple Pay sheet before authorizing payment.
• Add regression coverage that dismisses the actual presented Checkout Kit controllers and exercises native Apple Pay's dismissal state transition.

Accelerated Checkouts first shipped in v3.4. Through the end of v3, the behavior was:

Dismissal path	v3.4–v3.8 behavior
Close/swipe the Shop Pay Checkout Sheet	onCancel called
Close the Checkout Sheet shown as an Apple Pay fallback or thank-you page	onCancel called
Tap Cancel on the native Apple Pay sheet	onCancel not called

The first two paths were lost when the v4 presentation API stopped attaching a CheckoutDelegate, so restoring them repairs a v3 regression. Native Apple Pay used paymentAuthorizationControllerDidFinish(_:) to close its sheet but never forwarded that transition to the accelerated checkout callback.

That gap is now appropriate to close because v4 uses dismissal semantics rather than cancellation semantics. checkoutDidDismiss reports only that the buyer-facing accelerated checkout presentation has closed. It does not claim that a payment was cancelled, failed, or completed. When Apple Pay continues into a Checkout Kit fallback or thank-you page, dismissal is reported only after that final presentation closes.

How to test

GIVEN the Swift Accelerated Checkouts sample is configured with a test storefront, contains a cart item, and displays Shop Pay

WHEN the reviewer opens Shop Pay and closes or swipes down the Checkout Sheet

THEN the Xcode console should log 🚫 Checkout dismissed exactly once without logging a checkout failure

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GIVEN the Swift Accelerated Checkouts sample is running on a physical iOS device with Apple Pay configured and contains an Apple Pay-eligible cart item

WHEN the reviewer opens the native Apple Pay sheet and taps Cancel before authorizing payment

THEN the Xcode console should log 🚫 Checkout dismissed exactly once without reporting payment completion or checkout failure

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GIVEN the Swift Accelerated Checkouts sample is running on a physical iOS device with Apple Pay configured and Apple Pay continues into a Checkout Kit fallback or thank-you page

WHEN the reviewer closes that Checkout Kit presentation

THEN the Xcode console should log 🚫 Checkout dismissed exactly once when the final presentation closes

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Before you merge

Important

• I've added tests to support my implementation
• I have read and agree with the Contribution Guidelines
• I have read and agree with the Code of Conduct
• I've updated the relevant platform README (platforms/swift/README.md and/or platforms/android/README.md)

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Releasing a new Swift version?

• I have bumped the version in ShopifyCheckoutKit.podspec
• I have bumped the version in platforms/swift/Sources/ShopifyCheckoutKit/ShopifyCheckoutKit.swift
• I have updated the SwiftPM/CocoaPods version snippets in platforms/swift/README.md (major version only)

Releasing a new Embedded Checkout Protocol version?

• I have bumped embeddedCheckoutProtocolAndroid in platforms/android/gradle/libs.versions.toml
• I have updated protocol/languages/kotlin/embedded-checkout-protocol/api/embedded-checkout-protocol.api if the public API changed

Releasing a new Android version?

• I have bumped checkoutKitAndroid in platforms/android/gradle/libs.versions.toml
• I have updated the Gradle/Maven version snippets in platforms/android/README.md

Tip

See the Contributing documentation for the full release process per platform.