Request: return best LR without plotting

[BagelOrb]

Please make it possible to return the best learning rate without making a plot.

I suggest you refactor some code and pull the calculation of statistics out of the plotting function.

I think all of the statistics should be computed in the range_test function and I think the range_test function should return the optimal learning rate.

[ManuelZ]

To get the suggested LR:

lrs = np.array(lr_finder.history["lr"])
losses = np.array(lr_finder.history["loss"])

min_grad_idx = None
try:
    min_grad_idx = (np.gradient(np.array(losses))).argmin()
except ValueError:
    print("Failed to compute the gradients, there might not be enough points.")
if min_grad_idx is not None:
    best_lr = lrs[min_grad_idx]

print(f"Best lr:", best_lr)