test(targets,notify,audit): share a builder MockTarget testkit (#6717)

* test(targets): ship a builder MockTarget testkit and retire the in-crate Target mocks

Adds crates/targets/src/testkit.rs with a builder-style MockTarget implementing Target<E> for every E: PluginEvent, with orthogonal off-by-default knobs: disabled/active override, health delay plus health-started signal plus a drop-guard counter proving a cancelled probe future was dropped, an init failure budget (usize::MAX = always fail) plus blocking init plus an init counter, a close counter/signal/semaphore gate with a runtime block toggle, a save counter plus save failure budget, caller-supplied store and failed-store handles, and a shared final-failure counter. Clones and clone_dyn share all counters, so an observer clone keeps watching a target after it is boxed into a runtime.

The module is gated as #[cfg(any(test, feature = "test-support"))]: in-crate unit tests get it via cfg(test), and downstream test suites opt in through the new off-by-default test-support cargo feature (test-support = [], activating no dependencies).

Migrates the five in-crate duplicate mocks onto it: the plugin.rs registry-factory TestTarget, the runtime/adapter.rs lifecycle TestTarget (init/close/store knobs), the runtime/mod.rs TestTarget plus HealthDropGuard (close gating and health-probe tests), the target/mod.rs MoveTestTarget (folded into the test_support helper constructors used by the NATS JetStream failed-store tests), and the target/mod.rs StoreBackedTarget (the default send_from_store purge test; the mock deliberately does not override send_from_store or handle_terminal_failure). The forced init failure now uses TargetError::Initialization instead of the old adapter mock's Configuration; the adapter derives its redacted failure summary from the target id alone, so the migrated assertions are unchanged.

Leak guard: testkit unit tests assert the crate manifest still declares default = [] and that test-support = [] stays a pure cfg gate, complementing the compile-level cfg gate that keeps the mock out of production builds.

Part of rustfs/backlog#1846 (cluster 3, step 1).

* test(notify,audit): migrate the Target mocks onto the shared testkit

Retires the hand-written Target mocks in crates/notify and crates/audit in favor of rustfs_targets::testkit::MockTarget: notify's notifier.rs TestTarget/DeferredTestTarget/ClosableTestTarget, lifecycle.rs BlockingInitTarget/RetryInitTarget (rebuilt as observed MockTarget templates cloned by their plugin-descriptor factories, sharing the init signal, close counter, and single-failure init budget across generations), runtime_view.rs TestTarget, runtime_facade.rs TestTarget, and audit's pipeline.rs MockTarget, system.rs TestTarget, registry.rs CloseTestTarget, plus TestTarget and FailingTarget in audit/tests/pipeline_layer_test.rs. Removing the two integration-test mocks also removes their respelled PluginEvent bound (E: Send + Sync + 'static + Clone + Serialize + DeserializeOwned), which the plugin-contract rules require to be spelled only via PluginEvent.

lifecycle.rs ReplayTarget stays bespoke on purpose: its generation tags, mpsc observation channels, gated send_raw delivery, and ObservedQueueStore model the replay pipeline itself and would contort a general-purpose mock. The other bespoke mocks named out of scope in PR-3a (ProgrammedTarget, ClassifyingTarget, the ReloadableTargetTls fakes) are likewise untouched.

New testkit knobs, each defaulted off and unit-tested: with_id (rename a clone while keeping the shared counters, for factory templates), with_first_save_gate (the first save notifies entered and waits on release; several mocks may share one pair), with_health_gate (is_active waits on a release handle after notifying health_started), with_delivery_snapshot (fixed snapshot overriding the store-derived default), with_close_failures (close-failure budget, default TargetError::Storage) with with_close_failure_error to shape the variant (audit's registry test pins TargetError::Unknown), and an always-on is_enabled call counter exposed as enabled_call_count (notifier's generation tests count dispatcher selections through it).

Both crates enable the testkit through a dev-dependency on rustfs-targets with the test-support feature; the feature stays out of default and activates no dependencies, so production builds are unchanged.

Part of rustfs/backlog#1846 (cluster 3, step 2).

crates/targets/src/plugin.rs

@@ -421,61 +421,15 @@ where
 #[cfg(test)]
 mod tests {
     use super::{TargetPluginDescriptor, TargetPluginRegistry};
-    use crate::PluginEvent;
+    use crate::TargetError;
     use crate::runtime::adapter::BuiltinPluginRuntimeAdapter;
-    use crate::store::{Key, Store};
-    use crate::target::{EntityTarget, QueuedPayload, QueuedPayloadMeta};
-    use crate::{StoreError, Target, TargetError};
-    use async_trait::async_trait;
+    use crate::testkit::MockTarget;
     use rustfs_config::ENABLE_KEY;
     use rustfs_config::server_config::{Config, KVS};
     use std::collections::HashMap;
     use std::sync::Arc;
     use std::time::Duration;
 
-    #[derive(Clone)]
-    struct TestTarget {
-        id: crate::arn::TargetID,
-    }
-
-    #[async_trait]
-    impl<E> Target<E> for TestTarget
-    where
-        E: PluginEvent,
-    {
-        fn id(&self) -> crate::arn::TargetID {
-            self.id.clone()
-        }
-
-        async fn is_active(&self) -> Result<bool, TargetError> {
-            Ok(true)
-        }
-
-        async fn save(&self, _event: Arc<EntityTarget<E>>) -> Result<(), TargetError> {
-            Ok(())
-        }
-
-        async fn send_raw_from_store(&self, _key: Key, _body: Vec<u8>, _meta: QueuedPayloadMeta) -> Result<(), TargetError> {
-            Ok(())
-        }
-
-        async fn close(&self) -> Result<(), TargetError> {
-            Ok(())
-        }
-
-        fn store(&self) -> Option<&(dyn Store<QueuedPayload, Error = StoreError, Key = Key> + Send + Sync)> {
-            None
-        }
-
-        fn clone_dyn(&self) -> Box<dyn Target<E> + Send + Sync> {
-            Box::new(self.clone())
-        }
-
-        fn is_enabled(&self) -> bool {
-            true
-        }
-    }
-
     fn builtin_adapter() -> BuiltinPluginRuntimeAdapter<String> {
         BuiltinPluginRuntimeAdapter::new(
             Arc::new(|_event| Box::pin(async {})),
@@ -494,11 +448,7 @@ mod tests {
             "test",
             &[ENABLE_KEY, "endpoint"],
             |_config| Ok(()),
-            |id, _config| {
-                Ok(Box::new(TestTarget {
-                    id: crate::arn::TargetID::new(id, "test".to_string()),
-                }))
-            },
+            |id, _config| Ok(Box::new(MockTarget::new(&id, "test"))),
         ));
 
         let mut cfg = Config(HashMap::new());
@@ -532,11 +482,7 @@ mod tests {
                 target_type,
                 &[ENABLE_KEY, "endpoint"],
                 |_config| Ok(()),
-                move |id, _config| {
-                    Ok(Box::new(TestTarget {
-                        id: crate::arn::TargetID::new(id, target_type.to_string()),
-                    }))
-                },
+                move |id, _config| Ok(Box::new(MockTarget::new(&id, target_type))),
             ));
         }