Profile-Guided optimization(PGO) for the ethlambda binary

This issue tracks evaluating the impact of cargo pgo on the ethlambda binary.

While using rustc's native PGO workflow may ultimately provide better results, starting with cargo pgo offers a simpler path for initial evaluation.

One limitation is that PGO runs cannot currently be performed with jemalloc enabled, so the global allocator will need to be disabled for the profiling and optimized builds. This may offset some of the performance gains and should be taken into account when evaluating results.

It would also be useful to add a dedicated Criterion benchmark for ethlambda, making it easier to run consistent performance experiments and compare optimization strategies over time.

For reference, the rustc PGO workflow is documented here: https://doc.rust-lang.org/rustc/profile-guided-optimization.html

Start by locating the ethlambda binary configuration and existing benchmarks, then read the linked cargo pgo and rustc PGO documentation. Evaluate profiling and optimized builds with jemalloc disabled, and add a dedicated Criterion benchmark if the project supports it. Done means the impact is measured consistently and the results or limitations are recorded.