feat: Add some GitHub Classroom API endpoints

[jferrl]

Summary

This PR implements some GitHub Classroom API endpoints support by adding three new methods to the ClassroomService and fixes a deprecation warning in the addOptions function.

Changes Made

✨ New Features

1. GetClassroom Method

• Purpose: Retrieves a specific GitHub Classroom by ID for administrators
• API Endpoint: GET /classrooms/{classroom_id}

2. ListClassrooms Method

• Purpose: Lists all GitHub Classrooms for the current user
• API Endpoint: GET /classrooms

3. ListClassroomAssignments Method

• Purpose: Lists all assignments for a specific GitHub Classroom
• API Endpoint: GET /classrooms/{classroom_id}/assignments

Refactor

4. Reflect.Ptr Deprecation Fix

• Issue: Updated addOptions function to use reflect.Pointer instead of deprecated reflect.Ptr
• Change: Replaced reflect.Ptr with reflect.Pointer in github/github.go
• Benefit: Ensures compatibility with newer Go versions and removes deprecation warnings

Issue: #3684

[gmlewis]

@jferri - just FYI - I lost write access to this repo and this may cause unexpected delays for which I apologize.
You can watch that other PR to check on the status.

[jferrl]

@jferri - just FYI - I lost write access to this repo and this may cause unexpected delays for which I apologize. You can watch that other PR to check on the status.

No worries! 😃