Merge branch 'alin/MR-572-CallContextManager-stats' into 'master'

feat: [MR-572] Add response slot and memory reservation stats to `CallContextManager`

The equivalent stats are maintained by `CanisterQueues` (where they're just
some counters that cannot be validated). In `CallContextManager` we can have
direct debug_asserts to validate them against the actual counts of callbacks or
unresponded call contexts (and compute them from scratch on state loading).

And in-between rounds (or, more precisely, at the end of the round) we can
directly compare the two sets of stats (e.g. as part of the invariant check
that the scheduler performs). Plus initialize the `CanisterQueues` stats from
the `CallContextManager` stats on checkpoint loading (instead of blindly
persisting them). 

See merge request dfinity-lab/public/ic!18976

rs/execution_environment/src/canister_manager.rs

@@ -2533,9 +2533,18 @@ pub fn uninstall_canister(
                     // Cannot respond to system tasks. Nothing to do.
                 }
             }
+        }
 
-            // Mark the call context as responded to.
-            call_context.mark_responded();
+        // Mark all call contexts as responded to.
+        let call_context_ids = call_context_manager
+            .call_contexts()
+            .keys()
+            .cloned()
+            .collect::<Vec<_>>();
+        for call_context_id in call_context_ids {
+            call_context_manager
+                .mark_responded(call_context_id)
+                .unwrap(); // Safe to do, we only just collected the IDs above.
         }
     }
 

rs/replicated_state/src/canister_state/system_state.rs

@@ -1188,6 +1188,18 @@ impl SystemState {
 
     /// Returns the memory currently in use by the `SystemState`
     /// for canister messages.
+    ///
+    /// TODO(MR-572): Change this to:
+    ///
+    /// ++ N0: callbacks
+    /// -- N1: responses in input queues
+    /// -- 1:  if first item in task queue is a paused / aborted `Response`
+    /// ++ N2: requests in input queues
+    /// ++ N3: non-responded call contexts
+    /// ++ 1: if first item in task queue is an aborted `Request`
+    ///
+    ///  + S1: size of responses in output queues
+    ///  + S2: size of responses in input queues
     pub fn message_memory_usage(&self) -> NumBytes {
         (self.queues.memory_usage() as u64).into()
     }