refactor qwenimage pipeline tests to the new mixin structure (#14220)
* refactor qwenimage pipeline tests to the new mixin structure
* parametrize num_layers in qwenimage test dummy components for cache mixins
* drop faster cache test for qwenimage (unsupported by the model)
* restore test_inference and drop caching tests for qwenimage
* drop batch-single override in qwenimage tests, base tolerance covers it
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Co-authored-by: Sayak Paul <spsayakpaul@gmail.com>