Computes the f_beta between `preds` and `targets`

def fbeta(y_pred:Tensor, y_true:Tensor, thresh:float=0.2, beta:float=2, eps:float=1e-9, sigmoid:bool=True)->Rank0Tensor:
    "Computes the f_beta between `preds` and `targets`"
    beta2 = beta ** 2
    if sigmoid: y_pred = y_pred.sigmoid()
    y_pred = (y_pred>thresh).float()
    y_true = y_true.float()
    TP = (y_pred*y_true).sum(dim=1)
    prec = TP/(y_pred.sum(dim=1)+eps)
    rec = TP/(y_true.sum(dim=1)+eps)
    res = (prec*rec)/(prec*beta2+rec+eps)*(1+beta2)
    return res.mean()