fix: Recover unestablished MLS groups - WPB-21123

[acv-w]

WPB-21123 [iOS] Recover from having a local unestablished MLS group

Issue

An MLS conversation can remain in Core Crypto at epoch 0. Because conversationExists still returns true, the client incorrectly treats it as established when sending messages.

Before sending an MLS message, detect locally groups that have epoch 0, wipe them, and re-establish before encrypting and sending the message.

This PR also adds a developer flag, simulateUnestablishedMLSGroup, which leaves the next locally created MLS group at epoch 0 for manual reproduction and testing.

Testing

1. Enable simulateUnestablishedMLSGroup.
2. Create an MLS group.
3. Send the first message.
4. Verify the (epoch-0) group is wiped, re-established, and the message is sent successfully.

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Checklist

• Title contains a reference JIRA issue number like [WPB-XXX].
• Description is filled and free of optional paragraphs.
• Adds/updates automated tests.

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UI accessibility checklist

If your PR includes UI changes, please utilize this checklist:

• Make sure you use the API for UI elements that support large fonts.
• All colors are taken from WireDesign.ColorTheme or constructed using WireDesign.BaseColorPalette.
• New UI elements have Accessibility strings for VoiceOver.

[github-actions]

Test Results

1 247 tests   1 247 ✅  49s ⏱️
  155 suites      0 💤
    2 files        0 ❌

Results for commit 678161a.

♻️ This comment has been updated with latest results.

Summary: workflow run #29901708326
Allure report (download zip): html-report-32192-fix_recover-unestablished-mls-group-WPB-21123

[jullianm]

LGTM