Disable and warn on step tool usage after execution

[jpwilliams]

Summary

If a step.**() tool is called after a particular execution has finished, this means that some userland code is holding on to the reference and attempting to call it, which will always result in a hanging Promise being returned and very confusing results with the Executor.

This PR adds a small warning if this is detected.

Checklist

• Added a docs PR that references this PR N/A Internal
• Added unit/integration tests
• Added changesets if applicable

Related

• Would have helped debug SWEBench agent example agent-kit#23

[changeset-bot]

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Latest commit: 376032e

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