heartbeat: keep the master current through collection churn (#10657)

* heartbeat: name departed volumes in delta heartbeats

* master: release the lookup index with a deleted collection

* master: keep a fresh grow safe from the report that raced it

* volume: name the volumes a deleted collection took with it

Deleting a collection left the master to work out what went by omission from
the next full volume list, which it no longer gets: heartbeats carry the whole
list only when the master asks for it. The volumes a bucket's churn creates and
destroys between two of those requests are never named in either direction, so
the master keeps counting their slots as occupied and a cluster that creates
and drops collections quickly runs its free-slot accounting dry -- assigns fail
with no free volumes left while the disk holds a handful of volumes.

The destroy path already knows exactly which volumes it removed, so send them
down the same channel every other deletion uses.

* rust: name the volumes a deleted collection took with it

Mirrors the Go volume server. The notify path derives its deltas by diffing
snapshots, so a collection delete that does not wake it is invisible until the
master next asks for the whole list.

seaweed-volume/src/server/grpc_server.rs

@@ -660,10 +660,17 @@ impl VolumeServer for VolumeGrpcService {
     ) -> Result<Response<volume_server_pb::DeleteCollectionResponse>, Status> {
         self.check_grpc_admin_auth(&request)?;
         let collection = &request.into_inner().collection;
-        let mut store = self.state.store.write().unwrap();
-        store
-            .delete_collection(collection)
-            .map_err(|e| Status::internal(e))?;
+        {
+            let mut store = self.state.store.write().unwrap();
+            store
+                .delete_collection(collection)
+                .map_err(|e| Status::internal(e))?;
+        }
+        // The delta the notify path derives is the only thing that tells the
+        // master these slots came free: a heartbeat carries the whole list only
+        // when the master asks, and a volume grown and destroyed between two of
+        // them was never in one at all.
+        self.state.volume_state_notify.notify_one();
         Ok(Response::new(volume_server_pb::DeleteCollectionResponse {}))
     }