using loadFile or loadMem freeze the UI

[alnitak]

Description

After removing AudioIsolate there was the need to use a callback in C to tell Dart that the file was loaded. This make the load file functions to run in the main UI thread and using a C++ thread to do that, didn't work as expected.

This has been resolved using compute() to load files. On web there is still a freeze during loadMem()

Type of Change

• ✨ New feature (non-breaking change which adds functionality)
• 🛠️ Bug fix (non-breaking change which fixes an issue)
• ❌ Breaking change (fix or feature that would cause existing functionality to change)
• 🧹 Code refactor
• ✅ Build configuration change
• 📝 Documentation
• 🗑️ Chore