Fix(Heatmap): State updation is common for all users

[narainkarthikv]

Currently, the Heatmap component updates the state for all users rather than individual users. This can lead to data inconsistencies and a poor user experience, as changes made by one user can affect the displayed data for others.

Tasks

• Review the State Management Logic
  Investigate how the state is being managed and updated in the heatMapSlice and HeatMap component.

• Implement User-Specific Data Handling
  Modify the existing logic in the heatMapSlice to ensure that the state is updated only for the currently authenticated user based on their user ID.
  Ensure that each user's data is fetched and stored separately.

• Update Async Thunks
  Check the fetchMonthData and addExercise async thunks to ensure that they correctly handle and return data specific to the logged-in user.

• Test Functionality
  Test the Heatmap functionality with multiple user accounts to verify that state updates are user-specific and that one user's data does not affect another's.

• Documentation
  Update any relevant documentation or comments within the codebase to reflect the changes made for user-specific state management.