Specifiying hyperparameters in autokoopman function

[TUMcps]

I think we should use the same method for specifying values and ranges for all hyperparameters (n_obs, rank, lengthscale, enc_dim, n_layers). Currently this is in my opinion quite inconsistent since for n_obs one for example specifies the maximum number tried, while for rank one has to specify the range and gets an error when one tries to use a fixed rank. I would propose that for all hyperparameters one can either specify a single value, a range (start, stop), or a range with step size (start, stop, step).

[EthanJamesLew]

I fixed n_obs and rank. I don't think it makes sense to have lengthscale in the form of (start, stop, step) because it's a continuous hyperparameter (just (start, stop)) and in logscale.