refactor(functional): import all from metric in nn

GitOrigin-RevId: 41ab78d78d712f65cb75b6eb686e1de00a23f318

imperative/python/megengine/functional/metric.py

@@ -15,6 +15,10 @@ from .elemwise import abs, maximum, minimum
 from .math import topk as _topk
 from .tensor import broadcast_to, transpose
 
+__all__ = [
+    "topk_accuracy",
+]
+
 
 def topk_accuracy(
     logits: Tensor, target: Tensor, topk: Union[int, Iterable[int]] = 1

imperative/python/megengine/functional/nn.py

@@ -1660,3 +1660,4 @@ warp_perspective = deprecated_func(
 )
 from .quantized import conv_bias_activation  # isort:skip
 from .loss import *  # isort:skip
+from .metric import *  # isort:skip