add Sigmoid activation

src/refiners/fluxion/layers/__init__.py

@@ -1,4 +1,4 @@
-from refiners.fluxion.layers.activations import GLU, SiLU, ReLU, ApproximateGeLU, GeLU
+from refiners.fluxion.layers.activations import GLU, SiLU, ReLU, ApproximateGeLU, GeLU, Sigmoid
 from refiners.fluxion.layers.norm import LayerNorm, GroupNorm, LayerNorm2d
 from refiners.fluxion.layers.attentions import Attention, SelfAttention, SelfAttention2d
 from refiners.fluxion.layers.basics import (
@@ -44,6 +44,7 @@ __all__ = [
     "SiLU",
     "ReLU",
     "ApproximateGeLU",
+    "Sigmoid",
     "Attention",
     "SelfAttention",
     "SelfAttention2d",

src/refiners/fluxion/layers/activations.py

@@ -46,6 +46,14 @@ class ApproximateGeLU(Activation):
         return x * sigmoid(1.702 * x)
 
 
+class Sigmoid(Activation):
+    def __init__(self) -> None:
+        super().__init__()
+
+    def forward(self, x: Tensor) -> Tensor:
+        return x.sigmoid()
+
+
 class GLU(Activation):
     """
     Gated Linear Unit activation layer.