Refactor: move native breadcrumbs sync to FFI/JNI

[buenaflor]

📜 Description

Part of FFI/JNI refactorings

💡 Motivation and Context

Partly completes #3204

💚 How did you test it?

Manual tests, integration test

📝 Checklist

• I reviewed submitted code
• I added tests to verify changes
• No new PII added or SDK only sends newly added PII if sendDefaultPii is enabled
• I updated the docs if needed
• All tests passing
• No breaking changes

🔮 Next steps

[github-actions]

🚨 Detected changes in high risk code 🚨

High-risk code has higher potential to break the SDK and may be hard to test. To prevent severe bugs, apply the rollout process for releasing such changes and be extra careful when changing and reviewing these files:

• packages/flutter/android/src/main/kotlin/io/sentry/flutter/SentryFlutterPlugin.kt

[codecov]

Codecov Report

❌ Patch coverage is 87.50000% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 88.16%. Comparing base (e80304a) to head (054c6ff).

Files with missing lines	Patch %	Lines
.../flutter/lib/src/native/sentry_native_channel.dart	60.00%	2 Missing ⚠️

Additional details and impacted files

@@                        Coverage Diff                        @@
##           enh/app-hang-ffi-jni-refactor    #3293      +/-   ##
=================================================================
- Coverage                          88.65%   88.16%   -0.49%     
=================================================================
  Files                                 99       99              
  Lines                               3534     3523      -11     
=================================================================
- Hits                                3133     3106      -27     
- Misses                               401      417      +16     

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