Add comprehensive unit tests for the LockFreeBatcher covering
AddNode/RemoveNode lifecycle, addToBatch routing (broadcast, targeted,
full update), processBatchedChanges deduplication, cleanup of offline
nodes, close/shutdown behavior, IsConnected state tracking, and
connected map consistency.
Add benchmarks for connection entry send, multi-channel send and
broadcast, peer diff computation, sentPeers updates, addToBatch at
various scales (10/100/1000 nodes), processBatchedChanges, broadcast
delivery, IsConnected lookups, connected map enumeration, connection
churn, and concurrent send+churn scenarios.
Widen setupBatcherWithTestData to accept testing.TB so benchmarks can
reuse the same database-backed test setup as unit tests.
