Vestigial functions

Few of the global methods are not used/called anywhere else in the code. I suppose they are all vestigial. Consider removing them to keep the code base clean.

minterpy/utils.py

• report_error

minterpy/jit_compiled_utils.py

• lp_norm_for_exponents
• compute_grad_c2c
• compute_grad_x2c

minterpy/core/utils.py

• get_partial_derivatives

minterpy/polynomials/lagrange_polynomial.py

• _union_of_exponents