Add ACVM witness generation benchmarks for a set of test programs

[TomAFrench]

It's very important for us to have performant ACVM execution as this is required to prevent witness generation from being a bottleneck for proof generation.

We currently have some minor benchmarking for ACVM execution in this file. This boils down to use essentially timing the CLI command nargo execute --force for 3 of our test functions.

This has a couple problems:

• nargo execute --force is recompiling the circuit from scratch each time so we're benchmarking much more than just execution speed
• We're running nargo in a subprocess so we don't get any useful data out of the flamegraph which is generated.

Ideally we would have benchmarks which would:

• Compile the circuit once and loads it into memory
• Runs the circuit using the ProgramExecutor as exposed by the nargo crate rather than relying on the CLI.
• Applies https://doc.rust-lang.org/stable/std/hint/fn.black_box.html to the circuit inputs.
• Generates a useful flamegraph which can be used to inform future ACVM optimisations.

We can do this for a single Noir program to begin with and then roll it out to a decently sized suite in future.