[PM-9423] observable user encryptor

[audreyality]

🎟️ Tracking

https://bitwarden.atlassian.net/browse/PM-9423

📔 Objective

Lift user key encryptor into an observable provided at construction time.

🦮 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

[codecov]

Codecov Report

Attention: Patch coverage is 90.90909% with 3 lines in your changes missing coverage. Please review.

Project coverage is 31.67%. Comparing base (84ee01c) to head (aeb3b55).
Report is 5 commits behind head on main.

Files	Patch %	Lines
...ore/src/strategies/forwarder-generator-strategy.ts	60.00%	2 Missing ⚠️
...ons/history/src/local-generator-history.service.ts	80.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #10271      +/-   ##
==========================================
- Coverage   31.67%   31.67%   -0.01%     
==========================================
  Files        2623     2623              
  Lines       79418    79421       +3     
  Branches    14974    14974              
==========================================
- Hits        25159    25153       -6     
- Misses      52305    52313       +8     
- Partials     1954     1955       +1     

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