Derive `Default` for `GenesisJson` #5800

Job	Run time
dojo-core-test	12m 14s
test	12m 50s
docs	2m 24s
clippy	16m 36s
dojo-spawn-and-move-example-test	4m 20s
dojo-world-bindings-check	7m 0s
ensure-wasm	1m 36s
ensure-windows	6m 59s
fmt	1m 14s
test-hurl	5m 55s
	1h 11m 8s

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