test : added unit tests for TimeTrackingManager core methods

[tmdeveloper007]

Summary of What Has Been Done

Added comprehensive pytest unit tests for TimeTrackingManager in tests/test_time_tracking.py.

Changes Made

• TestSessionLifecycle: tests for start_session(), end_session(), and session state transitions
• TestTimeCalculations: tests for get_time_spent_on_item(), get_user_total_time(), and get_user_time_by_type()
• TestTimeEstimates: tests for estimate_time_for_item() with lesson, project, and unknown types
• TestLearningVelocity: tests for calculate_learning_velocity() with zero sessions
• TestCompletionEstimates: tests for estimate_completion_time() with and without history
• TestTimeAnalytics: tests for get_time_analytics() including session count and averages
• TestSkillProficiencyPrediction: tests for predict_skill_proficiency() including target_reached status

Impact it Made

Ensures time tracking and learning analytics features are accurate and reliable.

Note: Please assign this PR to the tmdeveloper007 account.

Closes #1315

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