Updated error formatting and tests for Python API

[fumedev]

UPDATED

• Modified the error formatting in the Python API by removing the import statement for numpy in the _format_approx function and replacing uses of np.inf with math.inf.

REFACTORED

• Split the test_error_messages test in the TestApprox class in testing/test_python_api.py into two separate tests: one for scalars and lists without numpy dependency, and another for numpy arrays that skips the test if numpy is not installed. Included necessary adjustments in the test file paths for better organization.