fix(llc): fix pinned message get duplicated

[VladShturma]

Github Issue: #2013

CLA

• I have signed the Stream CLA (required).
• The code changes follow best practices
• Code changes are tested (add some information if not applicable)

Description of the pull request

If you pin message, channel.state.pinnedMessages starts to store message twice. There already was a fix for such an issue, but for some reason it was overwritten later. I reapplied it and also added test

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 63.21%. Comparing base (30c106e) to head (efbc7ba).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2252      +/-   ##
==========================================
+ Coverage   63.17%   63.21%   +0.03%     
==========================================
  Files         402      402              
  Lines       25229    25224       -5     
==========================================
+ Hits        15939    15945       +6     
+ Misses       9290     9279      -11     

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[xsahil03x]

Hey @VladShturma , Thank you for the PR.

Can you fix the formatting issues and add additional tests for cases like:

1: When a already pinned message is updated (should not add duplicate)
2: When a already pinned message is updated with pinned: false (should unpin the pinned message)

[Copilot]

Pull Request Overview

This PR addresses the duplicated pinned message issue by removing the redundant logic that added messages to pinnedMessages and adds a corresponding test to verify the fix.

• Removed the code that manually appended pinned messages in ChannelClientState.
• Added tests to ensure that a pinned message is only added once.
• Updated the CHANGELOG to reflect the bug fix.

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
packages/stream_chat/test/src/client/channel_test.dart	Added tests for the messageUpdated event to verify pinned behavior.
packages/stream_chat/lib/src/client/channel.dart	Removed duplicate logic that led to inherent message duplication.
packages/stream_chat/CHANGELOG.md	Updated the changelog with a note of the bug fix.

[VladShturma]

Hello @xsahil03x
Done. I also added test to check that when not pinned message is updated with pinned: true it should not unpin another already pinned message.

[xsahil03x]

Hey @VladShturma LGTM, just added one comment

[VladShturma]

Hey @xsahil03x done