[Misc] cache result of disable_inplace

[bnellnm]

Purpose

Cache result of disable_inplace

cc @youkaichao , @mgoin , @ProExpertProg

Test Plan

Test Result

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• The purpose of the PR, such as "Fix some issue (link existing issues this PR will resolve)".
• The test plan, such as providing test command.
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[gemini-code-assist]

Code Review

This pull request aims to optimize the disable_inplace function by caching its result, which is a good performance improvement as the function's return value is constant during program execution. However, the implementation uses functools.cache, a feature introduced in Python 3.9. Since vLLM supports Python 3.8, this will lead to a runtime error. I've suggested a fix to use the compatible @functools.lru_cache(maxsize=None) decorator to ensure compatibility with Python 3.8.