feat: skip migration bundle mining in mobile

[begonaalvarezd]

Summary

Please summarize your changes, describing what they are and why they were made.

Adapt migration bundle mining warning for mobile: if firefly detects funds on one or more spent addresses, we recommend the user to use the desktop app to proceed with the migration, but we allow then to proceed and skip bundle mining

Also, there was a race condition in mobile when calling processMigratedTransactions account was undefined, leading to errors updating migratedTransactions.

Changelog

- feat: adapt bundle mining warning for mobile
- fix: migratedTransactions race condition unpopulated accounts

Relevant Issues

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Close #3804

Testing

Platforms

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• Desktop
  • [ ] MacOS
  • [ ] Linux
  • [ ] Windows
• Mobile
  • [ ] iOS
  • [x] Android

Instructions

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...

Checklist

Please tick all of the following boxes that are relevant to your changes.

• [x] I have followed the contribution guidelines for this project
• [x] I have performed a self-review of my own code
• [ ] I have commented my code, particularly in hard-to-understand areas
• [ ] I have added or modified tests that prove my changes work as intended
• [ ] I have verified that new and existing unit tests pass locally with my changes
• [ ] I have verified that my latest changes pass CI workflows for testing and linting
• [ ] I have made corresponding changes to the documentation