Migrate dft and pars to experimental new generic handling

[linusheck]

Adds a new generic handling that automatically generates instantiations for the given types and then puts a wrapper (in _template.py) around it to allow for this functionality:

# Readable aliases:
assert stormpy.dft._dft._DFT_Double is stormpy.dft.DFT[float]
assert stormpy.dft._dft._DFT_RationalFunction is stormpy.dft.DFT[stormpy.RationalFunction]

path = stormpy.examples.files.dft_json_and
double_dft = stormpy.dft.load_dft_json_file(path)
assert type(double_dft) is stormpy.dft.DFT[float]

rational_function_dft = stormpy.dft.load_parametric_dft_json_file(path)
assert type(rational_function_dft) is stormpy.dft.DFT[stormpy.RationalFunction]

# Construct a specialization explicitly:
explicit_builder = stormpy.dft.ExplicitDFTModelBuilder[float](double_dft)
assert type(explicit_builder) is stormpy.dft.ExplicitDFTModelBuilder[float]

# Or deduce the specialization from the constructor argument:
inferred_builder = stormpy.dft.ExplicitDFTModelBuilder(rational_function_dft)
assert type(inferred_builder) is stormpy.dft.ExplicitDFTModelBuilder[stormpy.RationalFunction]

# Overloaded functions call the specialization:
concrete_model = stormpy.dft.build_model(double_dft)
assert not concrete_model.supports_parameters

parametric_model = stormpy.dft.build_model(rational_function_dft)
assert parametric_model.supports_parameters

This replaces the custom Python wrapper functions that currently check input types.