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/tests/crates/cargo-c/src/main.rs

@@ -1,25 +1,25 @@
-//! Adds two numbers with a C function: `{"type": "add", "a", "b"}` -> `{"type": "sum", "value"}`.
-use sausage_actor::{json, messages, reply};
-
+//! SDK plugin linked to a WASI C function.
 unsafe extern "C" {
     fn c_add(a: i32, b: i32) -> i32;
 }
-
 fn add(a: i32, b: i32) -> i32 {
     unsafe { c_add(a, b) }
 }
-
-fn main() {
-    for message in messages() {
-        let (a, b) = (message.body["a"].as_i64().unwrap_or(0), message.body["b"].as_i64().unwrap_or(0));
-        let _ = reply(&message, json!({"type": "sum", "value": add(a as i32, b as i32)}));
+struct Plugin;
+#[sausage_plugin::rpc]
+impl Plugin {
+    /// Add two fixed numbers through C.
+    fn sum(&self) -> sausage_plugin::Result<i32> {
+        Ok(add(2, 3))
     }
 }
-
+fn main() {
+    sausage_plugin::run(Plugin);
+}
 #[cfg(test)]
 mod tests {
     #[test]
-    fn c_code_runs_on_the_host_target() {
+    fn c_code_runs_under_wasi() {
         assert_eq!(super::add(2, 3), 5);
     }
 }