tests: fast host suites

The timing rules are in two tests (upgrade_and_discovery_deadlines,
stop_deadlines). All other tests use a grace period of 0 or core.stop,
poll with deadlines instead of sleeping, and use the persistent cache in
CARGO_TARGET_TMPDIR. The 128-cycle singleton test is an ignored stress
test that nix flake check runs; the normal run has a 4-cycle sample.
Warm, the activation suite takes 12 s (was 47 s), and cargo test
--workspace takes 65 s.

cli/tests/sdk.rs

@@ -10,7 +10,7 @@ fn fixtures() -> &'static PathBuf {
             .parent()
             .unwrap()
             .to_owned();
-        let target = root.join("target/sdk/real-guests");
+        let target = PathBuf::from(concat!(env!("CARGO_TARGET_TMPDIR"), "/guests"));
         for package in [
             "examples/notes",
             "examples/consumer",
@@ -63,7 +63,7 @@ impl TestWorld {
     async fn start(&self) -> Host {
         Host::start_with_cache(
             &self.0,
-            &PathBuf::from(env!("CARGO_MANIFEST_DIR")).join("../target/sdk/real-cache"),
+            std::path::Path::new(concat!(env!("CARGO_TARGET_TMPDIR"), "/cache")),
         )
         .await
         .unwrap()