Function encode 

pub fn encode(event: &WalEvent) -> Result<Vec<u8>, EncodeError>

Encodes a WAL event into bytes.

The encoding includes:

• A 4-byte version header
• A 4-byte length frame
• A 4-byte CRC-32 checksum of the payload
• The postcard-serialized event payload

Determinism

This function produces deterministic output - the same event will always produce the same bytes. This is critical for replay and recovery.

Errors

Returns EncodeError::Serialization if the event cannot be serialized.