Update lagrange.rs

Moved shared logic into smaller reusable functions (compute_lagrange_coeff, compute_trivial_lagrange_coeffs, compute_nontrivial_lagrange_coeffs).
	•	Simplified logic and added descriptive function/variable names.
	•	Removed redundant comments, making the code self-explanatory.
	•	Minimized redundant computations by factoring out shared components.
	•	Added explicit panic with a clear message for out-of-range scenarios.
	•	Modularized test logic into test_range_lagrange_coeff for reusability.