Split and clean up GGUF quantization tests

[Isotr0py]

What does this PR do?

• Split up GGUF tests into three subsets: quantization tests, basic integration tests and models tests.
• This PR also consolidates the quantization tests since they are using duplicate code.

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@SunMarc @LysandreJik

[SunMarc]

Nice ! Thanks for the cleanup

[Isotr0py]

We use GGMLQuantizationType to make sure it's a validated "pure" quantization type, because some models like Q4_K_M means a combination of "mostly Q4_K" with some of other quantization, which shouldn't be used for quantization tests.

BTW, seems that this is causing tests_hub CI failing because gguf is not available on that CI, is there any way to solve this?

[SunMarc]

We shouldn't have this issue even if gguf is not available on the hub. There must be an issue when collecting tests with parameterized or maybe an issue with workflow of tests_hub. cc @ArthurZucker

Can you try to create a mapping instead so that you can replace GGMLQuantizationType by a string instead ?

[Isotr0py]

OK, let's use string for parameterize now! Also added a note to keep the quantization style aligned with gguf-py.

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