[BUG] Cutlass python epilogue doesn't work with BF16

Steps/Code to reproduce bug

import torch
import cutlass.epilogue


def epilogue(accum, bias):
    D = accum + bias
    return D

examples_tensors = dict(
    accum=torch.randn(1024, 1024),
    bias=torch.randn(1024, 1).bfloat16(),
    D=torch.randn(1024, 1024).bfloat16(),
)
cutlass.epilogue.trace(epilogue, examples_tensors)

Error

File ~/miniconda3/envs/dev_nightly/lib/python3.10/site-packages/cutlass/backend/evt/ir/load_nodes.py:187, in ColumnBroadcastImpl.argument_type.<locals>._Argument()
    184 class _Argument(ctypes.Structure):
    185     _fields_ = [
    186         ("ptr_col", ctypes.c_void_p),
--> 187         ("null_default", dtype2ctype[element_type]),
    188         ("dCol", tuple_type)
    189     ]
    190     def __init__(self, kwargs) -> None:
    191         ptr = kwargs[name]

KeyError: <DataType.bf16: 16>

Upon inspecting the code, I found that simply adding DataType.bf16: ctypes.c_uint16 to dtype2ctype will make things work. I verify that the outputs are correct.

https://github.com/NVIDIA/cutlass/blob/1ebda1ccef14df97da9ed098bd20e0c8520d6972/python/cutlass/backend/epilogue.py#L45-L51

Start with python/cutlass/backend/epilogue.py at the linked dtype2ctype mapping, then inspect the ColumnBroadcastImpl.argument_type path in python/cutlass/backend/evt/ir/load_nodes.py. Re-run the Python reproduction with BF16 tensors and verify that tracing completes without the KeyError and produces correct outputs.