[CIS-1522] Fix Memory Leaks when opening and closing channels

[nuno-vieira]

🔗 Issue Link

CIS-1522

🎯 Goal

The main goal was to fix the memory leaks around opening and closing channels which was mostly caused by the GalleryVC, but an overall cleanup of the memory leaks on the SDK was done as well.

🛠 Implementation

Break reference cycles in multiple places of the codebase.

📝 Changes

• Make sure to invalidate the URLSession in the URLWebSocketEngine. According to Apple, the URLSession.delegate is strongly retained and we need to make sure we call invalidateAndCancel() to clean up the URLSession.
• Fix Ref Cycle in GalleryVC.
• Fix multiple ref cycles in Updaters and Middlewares.
• Correctly unsubscribe from video player observers.
• Make sure to destroy the ChatClient in the LoginViewController so that is easier to analyse memory leaks
• Improve the feedback from the connection banner of the DemoApp

🎨 Changes

These are the instances that are retained after playing with the application and then coming back to the login screen before the fixes and after the fixes.

Before	After

🧪 Testing

• Run the DemoApp
• Select a User
• Open a Channel
• Scroll and open some images and videos
• Close a Channel
• Repeat the last 3 steps multiple times
• Logout
• Open the Memory Graph and observe the live instances

☑️ Contributor Checklist

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

🎉 GIF

[codecov]

Codecov Report

Merging #1812 (512f104) into develop (3370423) will decrease coverage by 0.12%.
The diff coverage is 72.72%.

@@             Coverage Diff             @@
##           develop    #1812      +/-   ##
===========================================
- Coverage    85.50%   85.37%   -0.13%     
===========================================
  Files          234      234              
  Lines        11314    11333      +19     
===========================================
+ Hits          9674     9676       +2     
- Misses        1640     1657      +17     

Flag	Coverage Δ
llc-tests	85.37% <72.72%> (-0.13%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
...ocketClient/Engine/URLSessionWebSocketEngine.swift	67.60% <70.00%> (-20.86%)	⬇️
...ventMiddlewares/TypingStartCleanupMiddleware.swift	100.00% <100.00%> (ø)
Sources/StreamChat/Workers/UserListUpdater.swift	84.21% <100.00%> (ø)

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[bielikb]

@nuno-vieira codecov reports quite huge decrease in the test coverage.

[adamrushy]

LGTM ✅

[nuno-vieira]

@nuno-vieira codecov reports quite huge decrease in the test coverage.

@bielikb The code coverage is decrasing 0.13%, it is minimal. (From 85.50% to 85.37%). This PR has a 72% coverage, of which the min is 85%. The reason is because URLSessionWebSocketEngine is not tested at all. It wasn't before, and I don't think it is worth adding tests for it, since it is just a wrapper for URLSession.