Add four unit tests guarding fixes introduced in recent commits:
- TestConnectionEntry_SendFastPath_TimerStopped: verifies the
time.NewTimer fix (H1) does not leak goroutines after many
fast-path sends on a buffered channel.
- TestBatcher_CloseWaitsForWorkers: verifies Close() blocks until all
worker goroutines exit (H3), preventing sends on torn-down channels.
- TestBatcher_CloseThenStartIsNoop: verifies the one-shot lifecycle
contract; Start() after Close() must not spawn new goroutines.
- TestBatcher_CloseStopsTicker: verifies Close() stops the internal
ticker to prevent resource leaks.
Updates #2545
8e26651f2c