Transforms Rust SDK: Add caching layer to Schema Registry client (LRU)

[oleiman]

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Backports Required

• [x] none - not a bug fix
• [ ] none - this is a backport
• [ ] none - issue does not exist in previous branches
• [ ] none - papercut/not impactful enough to backport
• [ ] v24.1.x
• [ ] v23.3.x
• [ ] v23.2.x

Release Notes

Improvements

• Add an LRU caching layer to Rust transform SDK Schema Registry client

[oleiman]

@rockwotj - this has been hangin' out for a little bit. back burnered for things with core dependencies. would be interested to hear your thoughts. particularly on the unfortunate reality of making mut& infecting everything 🤷

[rockwotj]

I will take a closer look next week. We should do LRU caching, but should consider interior mutability if this design is too invasive: https://doc.rust-lang.org/book/ch15-05-interior-mutability.html

[oleiman]

I will take a closer look next week. We should do LRU caching, but should consider interior mutability if this design is too invasive: https://doc.rust-lang.org/book/ch15-05-interior-mutability.html

Ah yeah, that's what i was looking for but didn't find. Nice one, thanks!

[oleiman]

force push contents:

• move cache code into sr crate and make private
• remove unnecessary Cache trait
• s/UnsafeCell/RefCell/ and minor changes to make copacetic
• remove some unnecessary copies

[oleiman]

force push CR changes