feat: add eth_chain_id to Kakarot contract

[ClementWalter]

Feature Request

Describe the Feature Request

Add a @view function to retrieve the chain_id of Kakarot. The Kakarot chain_id is actually the underlying Starknet chain id but modulo 2**32. This operation would be better done only once at the Kakarot level.

What

Add

@view
func eth_chain_id{syscall_ptr: felt*, pedersen_ptr: HashBuiltin*, range_check_ptr}() -> (
    chain_id: felt,
) {
    let (tx_info) = get_tx_info();
    let (_, chain_id) = unsigned_div_rem(tx_info.chain_id, 2 ** 32);
    return (chain_id=chain_id);
}

to kakarot.cairo and use IKakarot.eth_chain_id everywhere