Tests

Add `pad_to_aspect_ratio` flag to ImageConverter #6893

Job	Run time
Check the code format	1m 50s
Test the code (tensorflow, keras-stable)	25m 59s
Test the code (jax, keras-stable)	34m 10s
Test the code (torch, keras-stable)	16m 3s
Test the code (jax, keras-3.5)	32m 3s
Test the code (jax, keras-nightly)	34m 45s
	2h 24m 50s

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