Add some talk descriptions

Author: zliu41

uplc2025/_talks/jai.md

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+Making imperative thinking run efficiently on a functional runtime: tooling for high-performance Plutus.

uplc2025/_talks/zk.md

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+How to set up a Plutus project and verify zk proofs on chain with https://github.com/input-output-hk/plutus-halo2-verifier-gen