fix: add mising imports Update bench.rs

[moshderte]

Description: This PR resolves two compilation errors in the Plonk benchmarking code by adding the necessary use statements: The call to jf_utils::test_rng() requires importing test_rng from the jf_utils crate.

The use of vec![] inside the plonk_batch_verify_bench! macro requires importing std::vec (or using the fully qualified std::vec![]).

Without these imports, the compiler reports “undeclared crate or module jf_utils” and “cannot find macro vec”.

This patch adds the missing use declarations so that the code compiles successfully.

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