Cancel native KCL tasks with Python callers

[JordanNoone]

Cancelling a Python KCL call dropped its waiter but left the spawned native task running. Abort that task when spawn_py is dropped so cancellation reaches native execution and releases its owned connection.

Addresses #13858. The regression fails on main and passes with this change. A separate check through the real Python binding and a local fake Engine reproduced a surviving socket and heartbeat before the fix; afterward the socket closed in approximately 1 ms with no further messages. Real Engine geometry interruption and GPU release remain unverified.

[vercel]

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Project	Deployment	Actions	Updated
modeling-app	Ready	Preview	Sep 13, 2026 9:14am UTC

[codspeed-hq]

Merging this PR will not alter performance

✅ 150 untouched benchmarks
⏩ 128 skipped benchmarks¹

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_{Comparing codex/cancel-native-kcl-task (94ba891) with main (081a5bf)²}

Footnotes

1. 128 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

2. No successful run was found on main (9b0eced) during the generation of this report, so 081a5bf was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩