Windsock move to bench

[rukai]

This PR:

• Moves windsock to be a cargo bench instead of a cargo example.
  • This is a prereq for running in nextest: windsock: nextest compatibility #1295
• Uses the prebuilt shotover that cargo benches get access to skip the step of running cargo build in every windsock benchmark.
  • This should save about 0.5s per bench.
  • As a result we can delete shotover-proxy/build.rs as we no longer need access to PROFILE.

In order to ensure we always call with_bin to use the prebuilt shotover, I moved shotover startup into a new shotover_process helper.