feat(nns): Move neuron validation to timer (#3181)

We prefer timer to heartbeat in general, and the neuron validation can
be scheduled in a fixed interval. Therefore we should just move it to
timer as a low hanging fruit.

rs/nns/governance/canister/canister.rs

@@ -168,6 +168,7 @@ fn schedule_timers() {
     schedule_prune_following(Duration::from_secs(0), Bound::Unbounded);
     schedule_spawn_neurons();
     schedule_unstake_maturity_of_dissolved_neurons();
+    schedule_neuron_data_validation();
     schedule_vote_processing();
 
     // TODO(NNS1-3446): Delete. (This only needs to be run once, but can safely be run multiple times).
@@ -314,6 +315,13 @@ fn schedule_unstake_maturity_of_dissolved_neurons() {
     });
 }
 
+const NEURON_DATA_VALIDATION_INTERNVAL: Duration = Duration::from_secs(5);
+fn schedule_neuron_data_validation() {
+    ic_cdk_timers::set_timer_interval(NEURON_DATA_VALIDATION_INTERNVAL, || {
+        governance_mut().maybe_run_validations();
+    });
+}
+
 /// The interval at which the voting state machines are processed.
 const VOTE_PROCESSING_INTERVAL: Duration = Duration::from_secs(3);
 

rs/nns/governance/src/governance.rs

@@ -6632,15 +6632,6 @@ impl Governance {
         ));
     }
 
-    fn maybe_run_validations(&mut self) {
-        // Running validations might increase heap size. Do not run it when heap should not grow.
-        if self.check_heap_can_grow().is_err() {
-            return;
-        }
-        self.neuron_data_validator
-            .maybe_validate(self.env.now(), &self.neuron_store);
-    }
-
     /// Increment neuron allowances if enough time has passed.
     fn maybe_increase_neuron_allowances(&mut self) {
         // We  increase the allowance over the maximum per hour to account
@@ -6739,7 +6730,6 @@ impl Governance {
 
         self.maybe_gc();
         self.maybe_run_migrations();
-        self.maybe_run_validations();
         self.maybe_increase_neuron_allowances();
     }
 
@@ -6810,6 +6800,15 @@ impl Governance {
         Ok(())
     }
 
+    pub fn maybe_run_validations(&mut self) {
+        // Running validations might increase heap size. Do not run it when heap should not grow.
+        if self.check_heap_can_grow().is_err() {
+            return;
+        }
+        self.neuron_data_validator
+            .maybe_validate(self.env.now(), &self.neuron_store);
+    }
+
     /// Returns the 30-day average of the ICP/XDR conversion rate.
     ///
     /// Returns `None` if the data has not been fetched from the CMC canister yet.