[Kernel] Delegate construction of FusedMoEQuantConfig to FusedMoEMethodBase subclasses (#22537)

Signed-off-by: Bill Nell <bnell@redhat.com>

vllm/model_executor/layers/quantization/utils/fp8_utils.py

@@ -411,6 +411,7 @@ def per_token_group_quant_fp8(
         x_s = torch.empty(shape, device=x.device, dtype=torch.float32)
 
     # prefer CUDA kernel if available
+    # TODO(bnell): this causes some fp8 moe test to fail.
     if current_platform.is_cuda() and x.is_contiguous():
         torch.ops._C.per_token_group_fp8_quant(x, x_q, x_s, group_size, eps,
                                                fp8_min, fp8_max, use_ue8m0)