Fix: Circular queue display function null pointer dereference (#871)

[Akshatshukla-25]

Description

This PR addresses Bug 2 of issue #871. It adds a check to verify that queue_ptr->arr is not NULL before iterating and displaying elements inside display_circ_queue in src/data_structures/circular_queue.c.

Resolves

• Resolves part of Bug: Potential segmentation faults and crashes due to missing NULL checks and out-of-bound array writes #871 (Bug 2)

Changes

• circular_queue.c: Added queue_ptr->arr == NULL validation inside display_circ_queue.
• Makefile: Linked missing help objects to resolve test suite build errors (carried over to this branch).

Verification & Testing

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