Add React Native checkout preloading

[tiagocandido]

What changes are you making?

Adds React Native APIs and sample wiring for checkout preloading.

This exposes preload and cache invalidation through the React Native module, forwards the configuration flag to native SDKs, and updates the sample app to preload from the cart screen while invalidating when cart state changes.

How to test

• dev rn test js
• dev rn api check
• dev rn test android
• dev rn lint
• dev rn test ios

---

Before you merge

Important

• I have 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 have updated the relevant platform README (platforms/swift/README.md and/or platforms/android/README.md)

---

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 platforms/swift/CHANGELOG.md
• 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 platforms/android/CHANGELOG.md
• 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.

[github-actions]

React Native — Coverage Report

Lines	Statements	Branches	Functions
	91.83% (326/355)	87.98% (183/208)	100% (86/86)

[github-actions]

Package Size

Platform	Artifact	Base	Head	Delta
React Native	npm tarball	90.9 KiB	91.7 KiB	+841 B

Measured from the PR base SHA and PR head SHA. This comment reports package artifact sizes only; it is not a final app binary-size report.

[markmur]

Looks like we just need to check if preloading is enabled before calling the preload method, and add a test for the case but looks good otherwise 👍

[tiagocandido]

Looks like we just need to check if preloading is enabled before calling the preload method, and add a test for the case but looks good otherwise 👍

Done — preload() now checks the preloading config before calling native preload, and there’s coverage for the disabled case.