Fix: Radix sort negative value stack buffer overflow (#871)

[Akshatshukla-25]

Description

This PR addresses Bug 5 of issue #871. It adds a validation pass at the beginning of radix_sort inside src/advanced_sorting_algorithms/radix_sort.c to reject arrays containing negative values. This prevents counting sort from using negative indices which would cause out-of-bounds writes on the stack-allocated count array.

Resolves

• Resolves part of Bug: Potential segmentation faults and crashes due to missing NULL checks and out-of-bound array writes #871 (Bug 5)

Changes

• radix_sort.c: Validates that all elements inside the input array are non-negative.
• Makefile: Linked missing help objects to resolve test suite build errors (carried over to this branch).

Verification & Testing

• Ran make fmt to ensure style correctness.
• Compiled successfully with make.
• Ran and passed all unit tests with make test.