[PM-11133] Expand MainActor annotations

[KatherineInCode]

🎟️ Tracking

https://bitwarden.atlassian.net/browse/PM-11133

📔 Objective

This is part of the iOS 18 / Xcode 16 / Swift 6 effort

This adds @MainActor annotations to a number of protocols to eliminate Swift 6 errors. On the whole, these are delegate protocols between a Processor (which is @MainActor) and a Coordinator (which is @MainActor).

⏰ Reminders before review

• Contributor guidelines followed
• All formatters and local linters executed and passed
• Written new unit and / or integration tests where applicable
• Protected functional changes with optionality (feature flags)
• Used internationalization (i18n) for all UI strings
• CI builds passed
• Communicated to DevOps any deployment requirements
• Updated any necessary documentation (Confluence, contributing docs) or informed the documentation team

🦮 Reviewer guidelines

• 👍 (:+1:) or similar for great changes
• 📝 (:memo:) or ℹ️ (:information_source:) for notes or general info
• ❓ (:question:) for questions
• 🤔 (:thinking:) or 💭 (:thought_balloon:) for more open inquiry that's not quite a confirmed issue and could potentially benefit from discussion
• 🎨 (:art:) for suggestions / improvements
• ❌ (:x:) or ⚠️ (:warning:) for more significant problems or concerns needing attention
• 🌱 (:seedling:) or ♻️ (:recycle:) for future improvements or indications of technical debt
• ⛏ (:pick:) for minor or nitpick changes

[github-actions[bot]]

Checkmarx One – Scan Summary & Details – aea53999-ab62-4c3f-aba6-b7ca2356b528

No New Or Fixed Issues Found

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 88.61%. Comparing base (d0dc545) to head (cc3f98c). Report is 4 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #859 +/- ## ======================================= Coverage 88.61% 88.61% ======================================= Files 612 612 Lines 30520 30520 ======================================= Hits 27046 27046 Misses 3474 3474 ```

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