[fix][evaluation] clean up runs rejected before dispatch

[bitholic]

When run admission fails after creating a run and acquiring its mutex, the pending run and lock were left behind. This change shares pre-dispatch checks across Run and RetryItems, marks rejected runs failed before releasing the lock, and preserves the original error. Ambiguous MQ publication failures keep the lock.

Validation: eight regression scenarios, full evaluation service/application tests, go vet, and commercial integration build passed.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

@@            Coverage Diff             @@
##             main     #677      +/-   ##
==========================================
+ Coverage   78.84%   78.86%   +0.02%     
==========================================
  Files         707      707              
  Lines       87896    87928      +32     
==========================================
+ Hits        69298    69346      +48     
+ Misses      14607    14599       -8     
+ Partials     3991     3983       -8     

Flag	Coverage Δ
unittests	78.86% <100.00%> (+0.02%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
...ation/domain/service/expt_manage_execution_impl.go	84.05% <100.00%> (+1.49%)	⬆️

... and 2 files with indirect coverage changes

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