fix: internalize image off the main thread

[Phoenix1808]

When importing a selected image, internalizeUri() ran on the main thread: a ContentResolver query for the file name and a full file copy. For a large image or a slow document provider this can block the UI.

Make internalizeUri() a suspend function and move the two blocking calls to Dispatchers.IO, keeping the UI work on the main thread. The callers now invoke it from viewLifecycleOwner.lifecycleScope.

Issue: #21275

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First PR! 🚀 We sincerely appreciate that you have taken the time to propose a change to AnkiDroid! Please have patience with us as we are all volunteers - we will get to this as soon as possible.