CANN: add BF16 support for core operators (#20152)

CANN: add BF16 support for core operators (#20152)

* CANN: add BF16 support for core operators

Add BF16 (bfloat16) type support to the CANN backend for the following
operators: MUL_MAT, MUL_MAT_ID, GET_ROWS, SET_ROWS, CPY, CONT, and
OUT_PROD. This enables BF16 models to run on Ascend NPUs.

* CANN: skip NZ weight format for BF16 and add 310P compile guards

NZ weight format conversion does not support BF16 tensors, skip it
in set_tensor, get_alloc_size and mul_mat. Remove BF16 from MUL_MAT_ID
and OUT_PROD as there are no BF16 use cases. Add #ifndef ASCEND_310P
guards for all BF16 operator support since 310P does not support BF16.