feat: Add form lifecycle event bridge for in-app forms (#73)

[evan-masseau]

Summary

Adds form lifecycle event bridging to the Flutter SDK, enabling Dart consumers to receive a stream of events when in-app forms are shown, dismissed, or when a CTA button is clicked.

Changes

• New FormLifecycleEvent model — Dart sealed class with FormShown, FormDismissed, and FormCtaClicked subtypes, each carrying formId and formName, with CTA events also providing buttonLabel and deepLinkUrl
• New onFormLifecycleEvent stream on KlaviyoSdk — exposes lifecycle events via the existing EventChannel mechanism
• Platform integration:
  • iOS: Plugin registers with the Swift SDK's lifecycle handler on registerForInAppForms and unregisters on unregisterFromInAppForms, forwarding events through the Flutter event sink
  • Android: Plugin registers with the Android SDK's lifecycle handler on registerForInAppForms and unregisters on unregisterFromInAppForms, forwarding events through the Flutter event sink
• Lifecycle handler tied to forms registration — handler is automatically registered/unregistered alongside registerForInAppForms/unregisterFromInAppForms
• Example app Forms tab updated with a live lifecycle event log UI
• Native SDK dependencies temporarily unpinned for testing against unreleased native SDK builds

Test plan

• Unit tests for FormLifecycleEvent model parsing
• Verify lifecycle events stream correctly on iOS simulator
• Verify lifecycle events stream correctly on Android emulator
• Verify unregistering from forms also stops lifecycle events
• Verify example app event log populates on form show/dismiss/CTA click

Part of MAGE-287

Android	iOS

[evan-masseau]

Will need to update this with a proper SDK version once released obvs

[dan-peluso]

This is fine as it stands, since that wrapper is already a singleton and there's no side effects happening - but I think we should maybe add a comment somewhere that specifies if we add logic to the klaviyo native wrapper constructor then we have to revisit this

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