transformers

c1db3868 - [`Kernels Attention`] Change fallback logic to error out on explicit kernels request and include FA3 (#41010)

[`Kernels Attention`] Change fallback logic to error out on explicit kernels request and include FA3 (#41010) * fix * be more strict * change logic to include fa3 * fix the case where nothing is requested * modify old tests + add kernels related tests * style