cargo.build, the WASI test runner, the console, and core.notify ordering

- cargo.build (native): one source copy, tests under WASI, release
  build to /state/cargo/builds/<n>/, process groups killed on cancel.
  The host writes the SDK copy to /plugins/cargo/sdk/ at start.
- sausage test-runner: one instance per test, in parallel, with its own
  mount table (empty world, package folder at its path); answers
  core.lock, core.unlock, core.notify, core.log.
- The console: rustyline, notifications while typing, ls/cat through the
  process view, methods, ps, log, activate, revert, stop, kill.
- core.notify on stdout is handled in order, before the response.

cli/src/host.rs

@@ -82,6 +82,10 @@ impl Host {
             watcher: Mutex::new(None),
             retirements: Mutex::new(std::collections::HashSet::new()),
         }));
+        let cargo_world = host.0.world.clone();
+        let cargo =
+            tokio::task::spawn_blocking(move || crate::cargo::Cargo::new(cargo_world)).await??;
+        cargo.register(&host);
         host.boot().await?;
         Ok(host)
     }