[tests] refactor caching tests.

[sayakpaul]

What does this PR do?

• Refactor MagCache tests.
• Include TaylorSeer in our model-level caching test mixin.
• Consider removing caching-related mixins from test_pipelines_common.py.

[sayakpaul]

@DN6 LMK your thoughts on removing the caching-related stuff we have in test_pipelines_common.py. IMO, they're not adding much value given we have model-level caching testers for all the caching methods we support.

[sayakpaul]

@DN6 a gentle ping.

[HuggingFaceDocBuilderDev]

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[dg845]

Thanks for the PR! I think we should consider retaining the original MagCache tests in tests/hooks/test_mag_cache.py in some form, since if I understand correctly those tests are testing if the MagCache implementation is logically correct, while MagCacheTesterMixin is testing whether MagCache works with a given model.