dev: use Default implementation for GenesisJson

[tcoratger]

Describe Preferred Solution

After next release of Dojo and integration of dojoengine/dojo#1830, the

GenesisJson {
    // other fields
    .. Default::default()
}

pattern can be used to replace the following verbose construction:

kakarot-rpc/src/test_utils/katana/genesis.rs

Lines 320 to 339 in d2128cf

	Ok(GenesisJson {
	parent_hash: FieldElement::ZERO,
	state_root: FieldElement::ZERO,
	number: 0,
	timestamp: 0,
	sequencer_address: self.compute_starknet_address(self.coinbase)?,
	gas_prices: GasPrices::default(),
	classes: self.classes,
	fee_token: FeeTokenConfigJson {
	name: "Ether".to_string(),
	symbol: "ETH".to_string(),
	decimals: 18,
	storage: Some(self.fee_token_storage),
	address: None,
	class: None,
	},
	universal_deployer: None,
	accounts: self.accounts,
	contracts: self.contracts,
	})

[0xicosahedron]

can i work on this once release is done?

[tcoratger]

can i work on this once release is done?

Sure just assigned