Move per-node pending changes from a shared xsync.Map on the batcher
into multiChannelNodeConn, protected by a dedicated mutex. The new
appendPending/drainPending methods provide atomic append and drain
operations, eliminating data races in addToBatch and
processBatchedChanges.
Add sync.Once to multiChannelNodeConn.close() to make it idempotent,
preventing panics from concurrent close calls on the same channel.
Add started atomic.Bool to guard Start() against being called
multiple times, preventing orphaned goroutines.
Add comprehensive concurrency tests validating these changes.
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.
