chore: update Customer.io native SDKs (iOS 4.6.0, Android 4.19.0)

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Summary

Automated update of Customer.io native SDK dependencies:

• iOS SDK: 4.5.3 → 4.6.0 (Release Notes)

Key Changes

iOS SDK 4.6.0

4.6.0 (2026-07-06)

Features

• in-app: add dark mode support for in-app messages (#1131) (f92d058)

• Android SDK: 4.18.2 → 4.19.0 (Release Notes)

Android SDK 4.19.0

4.19.0 (2026-07-01)

Testing

• ✅ Flutter analysis passed
• ✅ Unit tests passed
• ✅ iOS compilation verified
• ✅ Android compilation verified
• ✅ Sample app builds successfully

Migration Notes

This update maintains API compatibility. Please test your integration thoroughly and review the release notes linked above for any specific changes that might affect your implementation.

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🤖 This PR was automatically generated and tested

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Note

Low Risk
Version-pin-only changes across Gradle, pubspec, and SPM; behavior shifts come from upstream SDK releases (notably iOS in-app dark mode), so integration smoke tests are the main check.

Overview
Bumps the Flutter plugin’s pinned Customer.io native SDK versions with no Dart or bridge API changes.

Android: cioVersion in android/build.gradle moves 4.18.2 → 4.19.0, so all io.customer.android:* artifacts (datapipelines, push FCM, in-app, optional location) resolve to the new release.

iOS: native_sdk_version in pubspec.yaml moves 4.5.3 → 4.6.0 (used by CocoaPods podspecs), and ios/customer_io/Package.swift pins the same exact customerio-ios version for SPM consumers.

Sample apps flutter_sample_cocoapods and flutter_sample_spm have refreshed pubspec.lock entries (path customer_io version and transitive resolution, including a tighter Dart SDK lower bound from pub get).

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