close method
Closes the sink.
The add method must not be called after this method.
Calling this method more than once is allowed, but does nothing.
Implementation
@override
void close() {
// Closing the sink doesn't necessarily close the underlying P2PStream here,
// as the stream's lifecycle is managed by the reserve method.
// If DelimitedWriter needs to signal end-of-writes, this might need to do more.
}