[trainer] fix: Import flash attn utils for Transformers higher than 4.55.0

[A1waysBeenHere]

Import the index_first_axis, pad_input, unpad_input, etc in a different way to handle the case for Transformers version higher than v4.55.0

Since the modification of PR40002 in Transformers, index_first_axis, pad_input, unpad_input have been moved to the transformers.modeling_falsh_attention_utils. The original import way for NPU cannot handle it.

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