Constant NON_FINALIZED_STATE_CHANGE_BUFFER_SIZE 

const NON_FINALIZED_STATE_CHANGE_BUFFER_SIZE: usize = _; // 2_000usize

How many non-finalized block references to buffer in NonFinalizedBlocksListener before blocking sends.

Correctness

This should be large enough to typically avoid blocking the sender when the non-finalized state is full so that the NonFinalizedBlocksListener reliably receives updates whenever the non-finalized state changes.

If the buffer does fill, sends apply backpressure (the sender awaits a free slot) rather than dropping blocks, so the listener still receives every block once the consumer catches up.