Function compute_events_hash 

pub fn compute_events_hash(
    batch_id: &str,
    source_node_id: &NodeId,
    sequence_start: u64,
    sequence_end: u64,
    created_at_ms: u64,
    previous_batch_hash: Option<&str>,
    events: &[Vec<u8>],
) -> String

Computes the SHA-256 hash of events payload deterministically including size prefixes and batch metadata.