refactor: migrate conversation core view models to metro [WPB-25946]

[Garzas]

https://wearezeta.atlassian.net/browse/WPB-25946

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PR Submission Checklist for internal contributors

• The PR Title

  • conforms to the style of semantic commits messages¹ supported in Wire's Github Workflow²
  • contains a reference JIRA issue number like SQPIT-764
  • answers the question: If merged, this PR will: ... ³

• The PR Description

  • is free of optional paragraphs and you have filled the relevant parts to the best of your ability

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What's new in this PR?

• Migrates core conversation screen ViewModels from Hilt call-site creation to Metro-backed factories.
• Covers messages, composer, drafts, send flow, attachments, and asset-related conversation core wiring.
• Keeps existing state/effect contracts and screen call sites behaviorally unchanged.

[codecov]

Codecov Report

❌ Patch coverage is 2.08333% with 141 lines in your changes missing coverage. Please review.
✅ Project coverage is 50.55%. Comparing base (0b602a2) to head (2b079df).

Files with missing lines	Patch %	Lines
.../conversations/ConversationCoreViewModelFactory.kt	0.00%	141 Missing ⚠️

❌ Your patch check has failed because the patch coverage (2.08%) is below the target coverage (80.00%). You can increase the patch coverage or adjust the target coverage.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #4893      +/-   ##
===========================================
- Coverage    50.88%   50.55%   -0.33%     
===========================================
  Files          619      620       +1     
  Lines        21803    21944     +141     
  Branches      3422     3422              
===========================================
  Hits         11094    11094              
- Misses        9683     9824     +141     
  Partials      1026     1026              

Files with missing lines	Coverage Δ
...rsations/attachment/MessageAttachmentsViewModel.kt	45.71% <ø> (ø)
...conversations/composer/MessageComposerViewModel.kt	75.26% <ø> (ø)
...rsations/messages/ConversationMessagesViewModel.kt	68.78% <ø> (ø)
...versations/messages/draft/MessageDraftViewModel.kt	69.44% <100.00%> (ø)
...s/messages/item/ConversationAssetPathsViewModel.kt	74.19% <100.00%> (ø)
...ations/migration/ConversationMigrationViewModel.kt	100.00% <100.00%> (ø)
.../conversations/sendmessage/SendMessageViewModel.kt	76.98% <ø> (ø)
.../conversations/ConversationCoreViewModelFactory.kt	0.00% <0.00%> (ø)

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[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud