test : added unit tests for CommunityManager core methods

[tmdeveloper007]

Summary of What Has Been Done

Added comprehensive pytest unit tests for CommunityManager in tests/test_community.py.

Changes Made

• TestDiscussion: tests for create_discussion(), reply_to_discussion(), and reply count tracking
• TestQuestions: tests for ask_question() and answer_question() with validation
• TestStudyGroups: tests for create_study_group() and join_study_group() including idempotency
• TestReputation: tests verifying reputation points are awarded correctly for each action type
• TestUserContributions: tests for get_user_contributions() breakdown
• TestTopContributors: tests for get_top_contributors() sorting and limit

Impact it Made

Ensures community features (discussions, Q&A, study groups, reputation) are reliable and regression-free.

Note: Please assign this PR to the tmdeveloper007 account.

Closes #1314

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