docs(langchain): correct import path in ModelCallLimitMiddleware docstring

[Kanav Bansal (bansalkanav)]

Summary

Updates the example in ModelCallLimitMiddleware docstring to use the correct import path. The previous import referenced a non-existent module, which could cause confusion for users following the documentation.

[corridor-security]

Summary: This PR only updates a docstring import path for ModelCallLimitMiddleware and does not modify runtime behavior or security-relevant logic.

Risk: Low risk. No new attack surface, data handling, authentication, or authorization changes were introduced; therefore, no exploitable vulnerabilities are present.

[codspeed-hq]

Merging this PR will not alter performance

✅ 2 untouched benchmarks
⏩ 13 skipped benchmarks¹

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_{Comparing bansalkanav:patch-7 (393cf33) with master (ee95ad6)²}

Footnotes

1. 13 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 master (8fec4e7) during the generation of this report, so ee95ad6 was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩

[Mason Daugherty (mdrxy)]

Thank you!