[Feature] [TheoreticalVariogram] [.autofit()] Add "safe" models as a one available parameter to choose from when checking theoretical models fit

[SimonMolinsky]

Is your feature request related to a problem? Please describe. The .autofit() method of the TheoreticalVariogram class takes an argument with model types to check which one describes data closely. The argument name Is model_types, and possible parameters are:

• 'all' - the same as list with all models
• 'circular'
• 'cubic'
• 'exponential'
• 'gaussian'
• 'linear'
• 'power'
• 'spherical'

There is no key to select only basic and safe model types.

Describe the solution you'd like Add the key safe that later checks those models: ["linear", "power", "spherical"]

Describe alternatives you've considered n/a

Additional context Compare it to the all key,