[PM-34106] chore: Consolidate KeychainItem into BitwardenKit via protocol

[KatherineInCode]

🎟️ Tracking

https://bitwarden.atlassian.net/browse/PM-34106

📔 Objective

This expands what was the KeychainStorageKeyPossessing protocol to include other properties from KeychainItem, and then renames it to KeychainItem while also renaming the former KeychainItem classes to BitwardenKeychainItem and AuthenticatorKeychainItem. This will make it easier to do further refactoring of our keychain code by making it easier to consolidate more things into BitwardenKit.

I considered turning this into a struct with extensions with static members, like FeatureFlag, but because many KeychainItem enum cases take an associated value (usually of the user ID), those would have to become static functions instead of static variables, and I wasn't particularly fond of that. However, I do think if we're good with the static functions, we could take that route instead, though I feel like it's six of one and half dozen of another.

[github-actions]

Checkmarx One – Scan Summary & Details – 895f600f-1e02-410d-adc8-e7cfa784f8bc

Great job! No new security vulnerabilities introduced in this pull request

[github-actions]

Overall Assessment: APPROVE

Reviewed the consolidation of KeychainStorageKeyPossessing into a richer KeychainItem protocol in BitwardenKit, adding accessControlFlags and protection properties alongside the existing unformattedKey. The rename of concrete enum types to BitwardenKeychainItem and AuthenticatorKeychainItem is applied consistently across all 17 changed files. Verified that the protection values on each concrete type match the previously hardcoded keychain accessibility constants, ensuring no behavioral change. The previous finding regarding the SharedKeychainItem.protection mismatch has been resolved.

Code Review Details

No findings.

[codecov]

Codecov Report

❌ Patch coverage is 71.42857% with 24 lines in your changes missing coverage. Please review.
✅ Project coverage is 85.80%. Comparing base (09df387) to head (c3526b1).
⚠️ Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
...Shared/Core/Auth/Services/KeychainRepository.swift	0.00%	13 Missing ⚠️
.../Services/TestHelpers/MockKeychainRepository.swift	0.00%	6 Missing ⚠️
...Shared/Core/Auth/Services/KeychainRepository.swift	75.00%	3 Missing ⚠️
...idgeKit/SharedKeychain/SharedKeychainStorage.swift	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2492      +/-   ##
==========================================
- Coverage   86.91%   85.80%   -1.11%     
==========================================
  Files        1846     2076     +230     
  Lines      163345   178294   +14949     
==========================================
+ Hits       141971   152989   +11018     
- Misses      21374    25305    +3931     

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