fix: clear execution references when engine run finishes

[saschabuehrle]

Fixes #1440

The execution engine retained internal references after completion (steps map, metadata, step state, fnArg, and the execution promise). In long-running processes this can keep step closures and large payloads reachable longer than necessary.

This adds a cleanup pass in the _start finally block to release those references once a run is finished, and includes a regression test that asserts the state is cleared after completion.

Greetings, saschabuehrle

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Note

Adds a releaseExecutionReferences() cleanup method called in the finally block of _start() to clear step maps, metadata, step state, fnArg, and the execution promise after a run finishes. Includes a regression test that casts to internal types to assert the cleared state.

^{Written by Mendral for commit 17ecdc2.}

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Latest commit: 17ecdc2

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[mendral-app]

LGTM

The cleanup is safe: it runs in the finally block after the core loop has fully resolved or errored, no external caller holds a reference to the execution object after start() completes, and all middleware hooks fire before the finally block. No correctness, data-loss, or security issues found.

_{Tag @mendral-app with feedback or questions. View session}

[fdarian]

It hasn't fixed the leak in my test, feel free to run against https://github.com/fdarian/inngest-memory-leak-repro

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