fix: illegal job sequence during barrier enter in router pickup

[atzoum]

Description

During router's pickup iteration, while trying to find an available worker slot, if the barrier forbids the job to enter, this job needs to be added to the blockedOrderKeys, so that no other job for the same ordering key can be picked up in this iteration.

Even though the barrier is synced only once before the router iterator's loop begins, the barrier's two limiters (concurrency & drain) are updated in realtime and can at any time fill or empty causing barrier#Enter's response to vary.

Linear Ticket

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Security

• The code changed/added as part of this pull request won't create any security issues with how the software is being used.

[codecov]

Codecov Report

Patch coverage: 100.00% and project coverage change: +0.25% 🎉

Comparison is base (c948122) 68.09% compared to head (750ae70) 68.35%.
Report is 3 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3737      +/-   ##
==========================================
+ Coverage   68.09%   68.35%   +0.25%     
==========================================
  Files         333      334       +1     
  Lines       51454    51517      +63     
==========================================
+ Hits        35038    35213     +175     
+ Misses      14133    14043      -90     
+ Partials     2283     2261      -22     

Files Changed	Coverage Δ
router/handle.go	73.20% <100.00%> (+0.71%)	⬆️

... and 28 files with indirect coverage changes

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