Claude Skill for benchmarks

[gabotechs]

This PR adds several improvements to the benchmarks:

• Claude Skills: adds some Claude Code skills for dealing with remote benchmarks. Typically these benchmarks take a while to execute, and analyzing the results can be a bit time consuming. This PR allows Claude to autonomously do all the tedious tasks of running benchmarks, waiting for the result, analyzing them, performing small changes, and redeploy for benchmark again.
• Adds ballista back: adds ballista benchmarks back so that we have another engine to compare to. This time, ballista is added in a cargo crate detached from the workspace, so users do not need to care about importing it. All the ballista code is pretty much what was removed from Remove ballista from benchmarks #292
• Stores the execution plans with metrics attached to the benchmarks run. This way, Claude can run benchmarks and analyze the execution plans along with the results in order to identify bottlenecks and improvement points.

[dd-annarose]

I looks good to me, but might need a more experienced eye to take a look!