Context

Refactor the connection pool's connection creation logic from a dedicated background goroutine loop into the semaphore-guarded spawning model outlined in PR #2098. This new design introduces aa connectionSem channel that enforces the maxConnecting limit by bounding the number of concurrent dial attempts. Instead of running long-lived workers, connection establishment is triggered opportunistically when new checkout requests are enqueued.

Note that this solution might improve GC under heavy load, as noted in GODRIVER-3419.

Definition of done

Re-open PR #2098 for review, update as needed.

Pitfalls

NA