[Background Mapping] Fix Mark as unread

[polqf]

🔗 Issue Links

Closes https://github.com/GetStream/ios-issues-tracking/issues/652

🎯 Goal

Fix Mark as unread when Background Mapping is enabled

📝 Summary

We need to use the data that the API Request returns to us, instead of waiting for the delegate calls.
The most important thing here is that we cannot use the delegate calls because we cannot know if the update is from a “mark as unread” action or a different thing. If we just update the unread banner on the delegate call, we lose all the context as the channel will be marked as read, and the views would then disappear.

🛠 Implementation

• The completion of markUnread(from:completion:) moves from just returning the Error to returning a Result object with the data.
• ChannelController.getFirstUnreadMessageId(for:) is now public
• Channel exposes now a convenience function to get the lastReadMessageId based on a user id (lastReadMessageId(userId:))

🧪 Manual Testing Notes

Precondition: BG Mapping Enabled

1. Open a channel with many messages
2. Mark a message as unread

Expected result:

• It should update the "Unread messages" banner to the right location

☑️ Contributor Checklist

• I have signed the Stream CLA (required)
• This change follows zero ⚠️ policy (required)
• This change should be manually QAed
• Changelog is updated with client-facing changes
• New code is covered by unit tests
• Comparison screenshots added for visual changes
• Affected documentation updated (docusaurus, tutorial, CMS)

🎁 Meme

[github-actions]

	1 Warning
⚠️	The changes should be manually QAed before the Pull Request will be merged

Generated by 🚫 Danger

[martinmitrevski]

LGTM codewise ✅ Only spotted one issue while testing (shared on Slack), not sure if it's related to BM. @testableapple should run a QA as well 🙏

[sonarqubecloud]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
44 Code Smells

90.7% Coverage
0.1% Duplication