Superfluous LightGBM Dependency Apple Silicon Incompatible

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This package requires lightgbm - which I can find no instance of being used in the code - however, this breaks the install on Apple silicon, e.g. there are no simple ways to install LightGBM on Mac M1/M2/M3.

If this unneeded dependency can be removed, I can simply pip install HEBO in my code once more!

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While lightgbm now supports apple silicon - this is still probably worth investigating, can we just remove the lightgbm dependency?