[CAMEL-20829] Streamline ServicePool synchronization

[gnodet]

As we've seen in recent PRs, ServicePool is over-synchronized, as when upgrading the cache
to use concurrent data structures, the old mechanism using a look was left in place.
Also, the lock when stopping was caused by trying to stop the service before removing
it from the queue (that was fix in a recent commit).

[github-actions]

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[davsclaus]

/component-test camel-ftp

Result ✅ The tests passed successfully

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