Replace the simple string-keyed inflight dictionaries with account-scoped
ConcurrentDictionary<string, Dictionary<string, InflightInfo>> structures.
Adds InflightInfo record with OpsCount for duplicate proposal tracking,
TrackInflight/RemoveInflight/IsInflight methods for streams and consumers,
and ClearAllInflight(). Updates existing Propose* methods to use $G account.
Go reference: jetstream_cluster.go:1193-1278.
63d4e43178