Implement server-side role checks and enhance result announcement API

[vikrantwiz02]

This pull request significantly improves the security and correctness of role-based access control throughout the examination and academic procedures APIs. Instead of relying on client-supplied role fields, the code now consistently checks the authenticated user's actual roles using helper functions, preventing privilege escalation and unauthorized access. Additionally, there are minor optimizations and new API endpoints added.

Role-based access control improvements:

• Replaced all checks of client-supplied role or Role fields with calls to user_holds_role or user_holds_any_role, ensuring authorization is always based on the authenticated user's actual roles in views.py [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24] [25].
• Updated the check_role utility in academic procedures to use the user's actual designations from the database, never trusting client input.

Performance and correctness improvements:

• Optimized result announcement queries in ResultAnnouncementListAPI by using select_related to avoid N+1 queries and fetch related batch and discipline data efficiently.

New API endpoints:

• Added two new endpoints to examination/api/urls.py: announcement-students/ and publish-result-selected/.

Other minor fixes:

• Added import of PublishedResultStudent and role helper functions to examination/api/views.py.
• Improved result announcement logic to check if results are actually published for a student before returning results.

These changes collectively harden the system against unauthorized access and improve maintainability by centralizing role-check logic.