Function softplus

pub fn softplus<const D: usize, B>(
    tensor: Tensor<B, D>,
    beta: f64,
) -> Tensor<B, D>
where
    B: Backend,

Applies the SoftPlus function element-wise.

softplus(x_i) = log(1 + exp(beta * x_i)) / beta

The SoftPlus function is a smooth approximation of the ReLU function.