feat: Add "Last Seen" and "Active Status" Feature for Direct Messages (DM)

[Favourrufus1]

What is the feature you would like to implement?

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Description:
We need to add a feature that shows the Last Seen and Active Status of users in Direct Messages (DM). This will help improve user engagement by showing when a user was last active or if they are currently online

Why is this feature important? The Last Seen and Active Status feature is important because:

1. Improves Engagement: Encourages timely interactions by showing when someone is online or was last active.
2. Better User Experience: Provides users with transparency about others' availability, reducing uncertainty.
3. Builds Trust: Makes users feel more connected and accountable in their interactions.
4. Privacy Control: Users can decide who sees their status, enhancing privacy.
5. Enhances Social Cues: Helps users gauge when to initiate conversations based on availability.
6. Competitive Edge: Keeps your platform competitive with features common in other messaging apps.
7. Aligns with Decentralization: Empowers users to control their own activity status without centralized control.

Will the protocol spec need to be updated?? Yes the protocol spec will need to be updated

How should this feature be built? (optional)

Requirements:

1. Track user activity, including message sending and other interactions.
2. Show Active Status as "Active now" or "Last seen <time ago>".
3. Store and retrieve user activity data (last seen timestamp and active status) in a decentralized manner.
4. Add privacy settings to control whether the last seen and active status are visible to others.
5. Update the DM interface to show the last seen and active status of users.

Acceptance Criteria:

• [ ] Implement a mechanism to track user activity (e.g., message sending, logins).
• [ ] Implement a periodic heartbeat system to track online status.
• [ ] Implement privacy settings to allow users to control visibility of their activity status.
• [ ] Show "Active now" or "Last seen <time ago>" in the DM interface.
• [ ] Ensure the feature works with both decentralized storage and blockchain.

Example Code:

• [ ] Add functionality to update user activity status when they send messages or interact with the app.
• [ ] Implement UI components to display the active status and last seen timestamp.
• [ ] Implement privacy controls for visibility of activity status.

Additional context

• The system must be designed in a decentralized way.
• Handle privacy and data storage carefully to ensure user security.

I'm willing to help with other parts of the implementation!

[sds]

This repository is for Farcaster, not Warpcast. Direct casts are not yet implemented in the protocol.