Use typed Android JSON-RPC params

[kiftio]

What changes are you making?

Replaces manual JSON field extraction logic in CheckoutProtocol and EmbeddedCheckoutProtocol with typed, serializable data classes (ReadyParams, CheckoutParams, ErrorParams, WindowOpenParams). Instead of casting JsonElement to JsonObject and manually extracting fields, params are now decoded directly via json.decodeFromJsonElement into the appropriate typed wrapper.

As a side effect, the ec.ready handler now treats non-string values in the delegate array (e.g. null, {}) as a parse error rather than silently ignoring them, which is reflected in the updated test expectations.

How to test

1. Run the Android unit tests to verify all existing and updated test cases pass:

   ./gradlew :lib:test
   

2. Verify that ec.ready with a mixed-type delegate array (e.g. ["window.open", null, {}]) now returns a JSON-RPC parse error (-32700) rather than a success response with partial results.
3. Verify that ec.error, ec.window.open_request, and checkout lifecycle events (ec.checkout.start, etc.) continue to decode correctly when valid params are provided, and return null gracefully on invalid input.

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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)

---

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 Android version?

• I have bumped the versionName in platforms/android/lib/build.gradle
• 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.

[kiftio]

Warning

This pull request is not mergeable via GitHub because a downstack PR is open. Once all requirements are satisfied, merge this PR as a stack on Graphite.
Learn more

• hide communication client #288
• remove buyer change in web #290
• Use typed Android JSON-RPC params #300 👈 (View in Graphite)
• Use typed Swift JSON-RPC envelopes #299
• respond to unknown requests with error #289
• ignore unknown messages #287
• main

This stack of pull requests is managed by Graphite. Learn more about stacking.

[github-actions]

React Native — Coverage Report

Lines	Statements	Branches	Functions
	91.66% (319/348)	87.86% (181/206)	100% (82/82)

[kiftio]

think we've lost some null safety here