[CLEAN] Synthetic Benchmark PR #30962 - Refactor FXIOS-12796 [Swift 6 Migration] Fix strict concurrency warnings in the CredentialsProvider

[tomerqodo]

Benchmark PR mozilla-mobile#30962

Type: Clean (correct implementation)

Original PR Title: Refactor FXIOS-12796 [Swift 6 Migration] Fix strict concurrency warnings in the CredentialsProvider
Original PR Description: ## 📜 Tickets
Jira ticket
Github issue

Also addresses FXIOS-13149.

💡 Description

Fix warnings in the CredentialsProvider.

See the unit testing slack channel for a Nov 26. demo on how to test the Credentials Provider feature (i.e. how to use Firefox as a password manager for Safari and for itself).

cc @Cramsden @lmarceau @dataports

📝 Checklist

• I filled in the ticket numbers and a description of my work
• I updated the PR name to follow our PR naming guidelines
• I ensured unit tests pass and wrote tests for new code
• If working on UI, I checked and implemented accessibility (Dynamic Text and VoiceOver)
• If adding telemetry, I read the data stewardship requirements and will request a data review
• If adding or modifying strings, I read the guidelines and will request a string review from l10n
• If needed, I updated documentation and added comments to complex code
  Original PR URL: Refactor FXIOS-12796 [Swift 6 Migration] Fix strict concurrency warnings in the CredentialsProvider mozilla-mobile/firefox-ios#30962