b11203

cuda: add F16 input to the FWHT (#29096)

• cuda: add F16 input to the FWHT

The CUDA FWHT accepts F32 input only. This makes the source type a template
parameter, so the kernel reads an F16 source directly instead of requiring a
converted copy. The F32 path is unchanged.

supports_op accepts an F16 src1 against an F32 src0 for the Hadamard hint.
Every other F16 src1 against a non-F16 src0 is still refused.

ggml_cuda_op_mul_mat_use_fwht is the single predicate both supports_op and
the dispatch call now share, checking contiguity and same-shape(src1, dst)
in addition to the type/hint conditions above. Without a shared predicate,
supports_op could admit an op that ggml_cuda_op_fwht then rejects only after
the unconditional same-shape assert has already fired; that gap predates
this change (it applies to the existing F32 path too) but this PR is what
touches supports_op, so it closes it here.

test-backend-ops on an A10 (lambdalabs): MUL_MAT 1297/1297, including all
24 Hadamard cases (18 existing F32, 6 new F16).

• cuda: use ggml_cuda_cast in the FWHT load, drop the comment

Website:

• https://llama.app

Attestations:

• https://github.com/ggml-org/llama.cpp/attestations/50458332

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