fix: use WeakMap in DerivedStateProvider to separate user state caches

[addisonbeck]

🎟️ Tracking

https://bitwarden.atlassian.net/browse/PM-15914

📔 Objective

When switching accounts derived state was still fetching from a cache for the
previous account, leading to UI elements being displayed with data from an
inactive account's cache. The DerivedStateProvider now uses a WeakMap to
maintain separate caches for each user's state Observable.

• Modifies DefaultDerivedStateProvider to use WeakMap for caching
• Each user's state Observable gets its own definition cache
• Added test to verify correct behavior during account switching
• Automatically cleans up inactive user caches on parentState change

⏰ 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]

Checkmarx One – Scan Summary & Details – b2b55602-12f5-439f-b6cc-5057d82bc363

Great job, no security vulnerabilities found in this Pull Request

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 34.29%. Comparing base (f44b36b) to head (2f0cee5).
Report is 9 commits behind head on main.

✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #12866   +/-   ##
=======================================
  Coverage   34.28%   34.29%           
=======================================
  Files        2934     2934           
  Lines       90225    90229    +4     
  Branches    16944    16945    +1     
=======================================
+ Hits        30937    30943    +6     
+ Misses      56824    56822    -2     
  Partials     2464     2464           

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