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.

interface/src/lib.rs

@@ -4,7 +4,7 @@
 pub mod compat;
 pub mod document;
 pub use document::Document;
-#[cfg(feature="codegen")]
+#[cfg(feature = "codegen")]
 mod client;
-#[cfg(feature="codegen")]
+#[cfg(feature = "codegen")]
 pub use client::client_rs;