Pre-compute pending build args outside state machine transaction

What does this MR do and why?

Re-roll of !223438 (closed) that will generalize for all enqueue actions.

Overrides Ci::Build's #save and #save! to pre-compute Ci::PendingBuild.args_from_build before the state machine opens a database transaction. The args are stored in transition.attributes and read by UpdateBuildQueueService#push inside the transaction, replacing the inline computation that previously held the transaction open during tag lookups, CI minutes checks, and plan lookups.

In AssignResourceFromResourceGroupService, switch from retry_lock_with_transaction to retry_lock so the before_transition callback runs outside the transaction boundary.

Both changes are gated behind the :precompute_pending_build_args feature flag.

References

Part of https://gitlab.com/gitlab-org/gitlab/-/work_items/589484

Screenshots or screen recordings

Before	After

How to set up and validate locally

1. With the flag disabled, run a pipeline with the following .gitlab-ci.yml

   # .gitlab-ci.yml
   simple_job:
     script: exit 0 # tests standard enqueue for regressions
   
   with_resource_group:
     resource_group: example-resource-group # tests the enqueue_waiting_for_resource changes
     script: exit 0

   • This establishes a baseline
2. In rails console enable the feature flag

   Feature.enable(:precompute_pending_build_args)

   For good measure, you should also restart rails, gdk restart rails. This ensures the feature flag is definitely active in sidekiq later.
3. Run another pipeline
   • This tests the new behaviors

Expected results: In both cases, jobs should complete successfully. This would mean each job successfully transitioned in and out of the pending state.

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