Corner orientation

[lispandfound]

This pull request includes changes to the source_modelling/sources.py file, focusing on refactoring and improving the robustness of the code, as well as adding new tests in the tests/test_sources.py file to ensure the correctness of the changes.

Refactoring and Improvements:

• Changed @staticmethod to @classmethod for factory methods in Point, Plane, and Fault classes, and replaced explicit class names with Self for better maintainability and readability. [1] [2] [3] [4] [5] [6] [7]
• Modified the Plane class constructor to validate the input bounds and ensure they form a valid plane.
• Updated length_m and width_m properties in the Plane class to explicitly return float values.
• Added numpy.typing as npt for type hinting in Plane class constructor.

Testing Enhancements:

• Added new tests in tests/test_sources.py to validate the Plane class constructor with various invalid inputs, ensuring that the constructor raises appropriate errors.

[lispandfound]

Since the last review:

1. I've added test cases to check that the Fault class actually rejects invalid faults.
2. Fixed the tests that were failing because of API changes introduced by Plane construction and extraction. #16.
3. Misc ruff fixes.

[joelridden]

Are they ever 0?

[lispandfound]

sometimes, when the fault is constructed dynamically in the case of the NSHMDB