Go like Scheduler, NativeCheck, http-check

[fabbing]

Summary

This PR bundles multiples changes around check execution:

• Add a reimplementation of the Go core-agent scheduler
  • The behavior is different in send_to_worker(), we would need sync:mpmc to exactly match the Go one. In the meantime, a pattern similar to what is done in work-stealing queue is used.
  • Need unit tests
• Add the lib/core-check library
  • Contain an interface for implementing Rust based checks, uncoupled from Saluki internals
  • Allow to also run these checks in the Go core-agent thanks to the Sink trait
  • Will be modified to implemented the Slim Check interface
• Add the NativeCheck type to run Rust based check, compiled in Saluki
• Modify the check trait
  • To allow use of async code in run()
  • Use interior mutability to access immutable fields via const reference (plays nicer with the scheduler)
• Add a reimplementation of the Python http_chunk, not exhaustive
• Add a feature flags for checks and python-checks
  • Needs to be threaded in the Makefile

Change Type

• Bug fix
• New feature
• Non-functional (chore, refactoring, docs)
• Performance

How did you test this PR?

References

[tobz]

Why are we doing this weird sharded scheduling bucket logic? If I add a check, having to wait up to interval_secs - 1 for it to start seems... terrible.

Maybe this matches the current Agent behavior, but if so, then I would say it's a poor design that we should not be emulating here short of a very good reason why it's absolutely required.