Girgitt/solar_fit_test

AI Summary: Refactor the Python code (`main.py`) for polynomial fitting of solar irradiance data. This involves extracting smaller, more focused functions from the existing `main.py` script to improve code readability, maintainability, and organization. The goal is to improve the overall code quality without altering the functionality.

AI Summary: Implement unit tests for the functions within the `main.py` and `utils.py` files of a Python project that performs polynomial fitting of sensor data. The tests should cover various scenarios and edge cases to ensure the accuracy and robustness of the data processing and model fitting.