Refactor & validate core components: Geometry, utilities, and testing

[alekfal]

• Add input data validation in current methods (use of pydantic or native python dataclasses)
• Update geometry.py module:
  • Use objects for point or bbox geometries.
  • Apply input validation (consider using a Pydantic model or a simple class abstraction for a structured codebase).
• Centralize constant global variables (such as DEFAULT_POWER_VARIABLES) and import them where nessesary.
• Create a utilities.py module for output preparation.
• Refactor tests to use fixtures and test case generators instead of manually written test cases.
• Update documentation to include the new changes and more examples.