Function block_and_size 

pub fn block_and_size<C>(
    chain: Option<C>,
    db: &ZebraDb,
    hash_or_height: HashOrHeight,
) -> Option<(Arc<Block>, usize)>
where
    C: AsRef<Chain>,

Returns the Block with block::Hash or Height, if it exists in the non-finalized chain or finalized db.