Rust client for pantsd

[benjyw]

Should greatly improve client overhead, making pants much snappier, and giving a much better user experience.

[stuhood]

Working on tackling this via #7369 due to the need to port options parsing incrementally.

[stuhood]

#7369 is paused for now due to the challenges of native deps (which we might eventually be able to remove, but not in the kind of timeframe we'd like for this effort).

In the meantime though, there are things that we can do to de-risk a full port of the client to rust, and to delete some python code that is now used only for pantsd. In particular: we can switch from using our python nailgun client to using the rust nails client. This will involve changing

pants/src/python/pants/bin/remote_pants_runner.py

Lines 168 to 177 in 9dd7328

	# Instantiate a NailgunClient.
	client = NailgunClient(
	port=port,
	remote_pid=pid,
	ins=self._stdin,
	out=self._stdout,
	err=self._stderr,
	exit_on_broken_pipe=True,
	metadata_base_dir=pantsd_handle.metadata_base_dir,
	)

to use a type exposed by the native_engine (similar to how we previously exposed the nailgun server).

This relates to #10057, because the python nailgun client does some peculiar things related to trying to delay sending signals to the server which can be made cleaner using async code.

[stuhood]

This landed in #10865 and again in #11147. Thanks @gshuflin!