setting default recommended device

[dtrawins]

🛠 Summary

Apply a naive approach for setting the default target device:
use discrete GPU if present
if several discrete GPUs present, use the one with the most free VRAM
if iGPU present and no discrete - use it
fallback to CPU if no GPU is present

🧪 Checklist

• Unit tests added.
• The documentation updated.
• Change follows security best practices.
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