Add benchmark for JITgen

[georgwiese]

Adds the benchmark I used for measuring the witness generation JIT in #2242.

[georgwiese]

Maybe it's late, but I don't know how to run this:

$ cargo bench --bench jit_witgen_benchmark
    Finished `bench` profile [optimized] target(s) in 0.48s
warning: the following packages contain code that will be rejected by a future version of Rust: mathru v0.6.10
note: to see what the problems were, use the option `--future-incompat-report`, or run `cargo report future-incompatibilities --id 1`
     Running benches/jit_witgen_benchmark.rs (target/release/deps/jit_witgen_benchmark-a4f413cc0aba77fb)

running 0 tests

test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s

[pacheco]

i think you have to add the bench to the Cargo.toml: check riscv/Cargo.toml for executor_benchmark

[georgwiese]

That worked, thanks!

[georgwiese]

Example run:
POWDR_JIT_OPT_LEVEL=1 cargo bench -p powdr-pipeline --bench jit_witgen_benchmark

On my machine, one iteration takes around 12.5s.

However, it seems like in CI, this is closer to 55s. On our server, the time for one iteration is around 62s.

Seems to be mostly compilation time.