worker: Extract enqueue_simple/deduplicated() fns

[Turbo87]

This reduces the amount of code that needs to be compiled for each BackgroundJob impl, since these inner enqueue() fns are not using generics.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 88.86%. Comparing base (261f91e) to head (a954e62).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #9630      +/-   ##
==========================================
+ Coverage   88.85%   88.86%   +0.01%     
==========================================
  Files         288      288              
  Lines       29222    29270      +48     
==========================================
+ Hits        25965    26012      +47     
- Misses       3257     3258       +1     

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