Use HFCompatibleLoRA instead of instance method replacement

[hmellor]

Follow up for suggestion mentioned in #13770 (comment)

Changes:

• Reverts changes made to layers.py
• Uses __class__ so that HFCompatibleLinear appears as vLLM layer (use __wrapper_class__ as a way to identify the true class)
• Add HFCompatibleLoRA which uses the same technique
• Replace use of deprecated Python 3.8 types in changed files

This means that when printing models or examining layers, type(layer) will return the inner layer, rather than HFCompatibleX. This stops the layer replacement from hiding the type of the original layer.

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[Isotr0py]

Thanks for the cleanup effort!

[hmellor]

After some more tinkering, it appears that __class__ cannot be used as I am attempting to use it in this PR. I'll close this and perhaps try an alternative method another time.