tests: add BF16 non-contig coverage for MUL_MAT permutations (#22689)

tests: add BF16 non-contig coverage for MUL_MAT permutations (#22689)

The MUL_MAT test loop iterates over base_types[] to generate non-contig
permutation cases (3 standard permutations across n in {1, 8, 16}).
BF16 is absent from base_types[], so these 9 cases were never generated
for BF16 even though every other type covered by base_types[] tests them.

Add the missing 9 cases explicitly: BF16 x F32, m=16, k=256, bs=[2,3],
permutations {0,2,1,3}, {0,1,3,2}, {0,3,2,1}, with n in {1, 8, 16}.

Suggested-by: @jeffbolznv