DataManager class and validators.py

[debpal]

This pull request includes:

• Introduction of validators.py, where a private function _variable_origin_static_type is added for checking the static type origin of input variables.
• Introduction of the DataManager class, with simulated_timeseries_df moved from the SensitivityAnalyzer class into this new class. In future, additional methods will be added to handle simulated data.
• Removal of several duplicate type-checking test functions, made redundant by the introduction of _variable_origin_static_type.
• Identification of several mypy errors in methods of the TxtinoutReader class. These were not fixed, as the methods are planned for removal in future versions.