Add Flutter hot reload on save action

[castletaste]

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Describe the feature

Hello!

I suggest implementing the "hot reload" function in Flutter to automatically update the app when changes are saved to the code

This will significantly speed up the development process and increase developer productivity, attracting the Flutter community to use Zed

more info about hot reload https://docs.flutter.dev/tools/hot-reload

If applicable, add mockups / screenshots to help present your vision of the feature