[Bugfix] Reenable LRU cache on Outlines' guide getters

[Lap1n]

In our setup, vLLM's structured generation became 2x slower from 0.5.2 to 0.5.3.

The regression was introduced with this commit. I replaced the LRUCache annotation on the _get_guide function of the LogitsProcessor in favor of the @cache implementation from Outlines, so the cache function outputs can be reused across startup. However, this seems to have a significant impact on performance as Outlines' diskcache-based implementation doesn't seem as fast.

This PR adds back the LRUCache on top of the Outlines one fixes this performance issue.

FIX #8307 (link existing issues this PR will resolve)

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[stas00]

I think other methods need caching as well - perhaps in another PR if it not a regression?

See the first item of #8313 (comment) - it rebuilds the json schema regex on every request!

edit: made a standalone issue #8383 so this doesn't get dropped

[Lap1n]

Nice findings! I guess those changes could be added in another PR. What do you think @robertgshaw2-neuralmagic ?

[akramsystems]

any updates on this PR