chore(TODO): Implement caching for ConsensusBlock size

[ikwuoz]

arc-node/crates/types/src/block.rs

Lines 55 to 58 in cf51a19

	pub fn size_bytes(&self) -> ByteSize {
	// TODO: Cache this
	ByteSize::b(block_as_ssz_data(self).ssz_bytes_len() as u64)
	}

Propose a caching implementation for ConsensusBlock size by:

• Introducing a new ConsensusBlock field cached_size_bytes of type OnceLock from std
• Lazily initialize this field on demand in size_bytes
• Update references to ConsensusBlock in codebase

[ikwuoz]

can you assign this issue to me?
@ZhiyuCircle