Add node to extend sigmas

[catboxanon]

This PR adds a node that will extend the sigma values for a given sigma range. This is exactly identical functionality to #7890 but now applicable to any sampler -- see that PR for more details.

[liesened]

Personally I don't agree on the naming, it's sort of out of place. I'd suggest renaming a bunch of things:

• expand -> extend
• ExpandSigmas -> ExtendIntermediateSigmas
• sigma_max -> start_at_sigma
• sigma_min -> end_at_sigma
• expanded_sigmas -> extended_sigmas

Also, I'd like to detach the interpolation space from the actual interpolation function, and introduce spacing input. This will make interpolating between steps using different functions easier to implement.

...

interpolator = {
    'linear': lambda x: x
    'cosine': lambda x: torch.sin(x*math.pi/2)
    'sine':   lambda x: 1 - torch.cos(x*math.pi/2)
}[spacing]

# linear space for our interpolation function
x = torch.linspace(0, 1, steps + 1)[1:-1]

for i in range(len(sigmas) - 1):

    ...

    if start_at_sigma <= sigma_current <= end_at_sigma:
        interpolated_steps = interpolator(x) * (sigma_next - sigma_current) + sigma_current
        extended_sigmas.extend(interpolated_steps.tolist())

...