Stop workers when job finalization fails

[rafael-pissardo]

Summary

• wrap finalization failures while a claimed execution is still present in a dedicated error
• stop the owning worker after that unrecoverable error so shutdown releases the claim for retry
• keep workers running after ordinary job failures and avoid joining from a pool thread

Fixes #748.

Test plan

• TARGET_DB=sqlite bundle exec ruby -Itest test/unit/worker_test.rb
• TARGET_DB=sqlite bundle exec ruby -Itest test/models/solid_queue/claimed_execution_test.rb
• TARGET_DB=sqlite bundle exec ruby -Itest test/integration/jobs_lifecycle_test.rb
• RuboCop on changed Ruby files